New descriptive astronomy

Material Information

New descriptive astronomy
Alternate title:
Story of the stars
Cover title:
Steele's sciences
Spine title:
Steele's new astronomy
Steele, Joel Dorman, 1836-1886
A.S. Barnes & Co ( Publisher )
Place of Publication:
New York
A.S. Barnes & Company.
Publication Date:
Physical Description:
xii, 326 p., [4] leaves of plates : ill. (some col.) ; 19 cm.


Subjects / Keywords:
Astronomy -- Juvenile literature ( lcsh )
Physical sciences -- Juvenile literature ( lcsh )
Textbooks -- 1884 ( rbgenr )
Bldn -- 1884
Textbooks ( rbgenr )
non-fiction ( marcgt )
Spatial Coverage:
United States -- New York -- New York
United States -- Illinois -- Chicago
Target Audience:
juvenile ( marctarget )


General Note:
Includes index.
Preservation and Access for American and British Children's Literature, 1870-1889 (NEH PA-50860-00).
Statement of Responsibility:
by Joel Dorman Steele.

Record Information

Source Institution:
University of Florida
Holding Location:
Baldwin Library of Historical Children's Literature in the Department of Special Collections and Area Studies, George A. Smathers Libraries, University of Florida
Rights Management:
This item is presumed to be in the public domain. The University of Florida George A. Smathers Libraries respect the intellectual property rights of others and do not claim any copyright interest in this item. Users of this work have responsibility for determining copyright status prior to reusing, publishing or reproducing this item for purposes other than what is allowed by fair use or other copyright exemptions. Any reuse of this item in excess of fair use or other copyright exemptions may require permission of the copyright holder. The Smathers Libraries would like to learn more about this item and invite individuals or organizations to contact The Department of Special and Area Studies Collections ( with any additional information they can provide.
Resource Identifier:
026966914 ( ALEPH )
ALH8301 ( NOTIS )
63674312 ( OCLC )

Full Text

R M-6lo
imm Me



r "



The Baldwin Library

i. ........... .


Llr- 4---C.~~

Ir P,,LC-~~z-


A~' C':' 2


d ~Pv'p

............ --- ------ .-..:::i:i.L-Iii;ii!!!A i@i .- ...
iririiiriirrr!iiiiiiiiiiiiiiii~ijiiii~ i~iiiiii 'i?.iiiiifiliiiiii"i-~~'-
............. .............. -.- ------i!i -+ --_. ..... ..... 7, -+ .-- -+ + + .:-. + --+ .

S;.-+.+.:2 _+.............
:. . . I-- ---..+ 'x:::: -.

............. ;H ---
.............. .
----- ----- -- .... ....... ------II =- -
............._... .......... ....... --------r... -- =-- --

......... .... + .-+ + +... ...................
++~~~~~~~~~.... ... :+ ... +B+#+++++ ++..
--------------- -- -ii
...........X -+:-::- .......... ..... --- ........ +::-:.:+:

~iiiiiiiiiiiiltiiiii _o ':-_ +:_.++i~i:i:;:-iiji
'I ......... ':,+- + ::i ---- -.

K i --" --"++ .. .. ...- .-H -
A- I ---------
...~ ... -- --- ... .fi. ...
w' ... -_ -- -..--......... ...
- - - . ..I I.I. - -
~;ii~i.:--1--iiiiiiiiir:;:;iciir iiiiri-------- -----------~;iiii

....... ....--.OR .OS .R A TEL..OE.... 8
- --------- --------- ............~::~i~iiii~i
.:iiit:~iiii :-iirti~iirii~ii..... .......i~l

ii.iiiiii1:Pj-:ilrL it -------liIIi iili:
.ii~iijiiiiiii~ijiiii~iiiiiirji-iliii~ii''i'~iiiiiiiaI;:ii~li;~i~i-ilifiiiiiii'!ifji~!i!ll~j~ii~iiii2.~1iii~itiliiiiin~Hiii iir ~ ~ ----- ----- 175:~i~iii
riiiiiiii" iii~ iii1"T .......~i~iiiii-iii~~:si:,'iiisii~iririr

il=:::-s t 'If-lIfujINKIIIII:
::i Iiiii:::::::-:tii~ iil~if ~ ~ 7 -- --------fi~ii
5 -Z- I ~_liJi~ _~iiiii~"i~i~i

~iiIiiiiil..iis4Ii~i j:~iiiii fi ii~ii'ifi-iii::~Ciii~;::7 ~ii~-~-;~:iii;-iiiii-iIli 11~i
iiI~~ji~iii~iiiiiiii iiiiiiiiiill-ii~i3Q iii iililt 1:i~'-ii~iiji~aiiii'i
il~ii::iiieiiiiei-iiiii iiiiiriiiiiiiiiii-:iiiiiiiiiii ~ _~~ii_-:-iiliii-i~-iti-i-i=~iiliiii!illI

I r








The hea:e2:c dcoi Ue t o go 'y of od.. anrd the r ta ent showeth
- aod>io ''-PSALM XIX, 1.

Copyright, 1869, 1884, by




J. DORMviAN SiTEELE, Pv-.D.. F4.G'S.,
i author oof the Fourteen WIeeks Series in iNVafral Srience. etcz, etc.

New Popular Chemistry. Ne \, F)eseriptivx A -troiomciy.

Nev Popular Phy.sis. Newv H-ycienic Phy-iology.

Nevw Popular Zoology. Popular Geoloqy.

An Introduction to Botany.

The Publishers can supply (to Teachers only) a Key containing An;wers to the
Questions and Problems in Steele's entire Series.



A Brief History of the United States.
A Brief History of France.
A Brief History of Ancient Peoples.
A Brief History of Medieval and Modern Peopies,
A Brief General History.

A Brief History of Greece.
A Brief History of Rome.
A Popular History of the United States.


TURING the past few years great advances
-D have been effected in astronomical science.
Physics has come to the help of Mathematics, and,
not content with the old question, where the heav-
enly bodies are, has sought to find out what they are.
Valuable discoveries have been made concerning
Meteors, Shooting Stars, the Constitution of the Sun,
the Motion of the Heavenly Bodies, &c. The investi-
gations connected with Spectrum Analysis have been
especially suggestive. On every hand the facts of
the New Astronomy have been accumulating. Until
recently, however, they were scattered through many
expensive books, and were consequently beyond the
reach of the most of our schools. It has been the
aim to collect in this little volume the most interest-
ing features of the larger works.
Believing that Natural Science is full of fascina-
tion, the author has sought to weave the story of
those far-distant worlds into a form that may attract
the attention and kindle the enthusiasm of the pupil.
This work is not written for the information of
scientific men, but for the inspiration of youth.


Therefore the pages are not burdened with a multi-
tude of figures which no memory could retain.
Mathematical tables and data, Questions for Re-
view, a very valuable Guide to the Constellations,
and an Apparatus for Illustrating Precession, are
given in the Appendix, where they may be useful
for reference.
Those persons having a small telescope will find
valuable assistance in the List of interesting Ob-
jects for a common Telescope." The Index contains
the pronunciation of many difficult names.
Particular attention is called to the method of
classifying the measurements of Space, and the
practical treatment of the subjects of Parallax, Har-
vest Moon, Eclipses, the Seasons, Phases of the Moon,
Time, Nebular Hypothesis, Spectrum Analysis, and
To teachers hitherto compelled to use a cumber-
some set of charts, it is hoped that the star maps
here offered will present a welcome substitute. The
geometrical figures, showing the actual appearance of
the constellations, will relieve the mind confused with
the idea of numberless rivers, serpents, and classical
heroes. Only the brightest stars are given, since in
practice it is found that pupils remember the general
outlines alone, while the details are soon forgotten.
Many of the cuts are copied from the French edi-
tion of Guillemin's "Heavens." Acknowledgment


for much valuable material is hereby made to this
excellent work, and also to "Chambers's Astron-
omy," "Newcomb's Astronomy," and Young's "The
Finally, the author commits this little work to the
hands of the young, to whose instruction he has con-
secrated the energies of his life, in the earnest hope
that, loving Nature in all her varied phases, they
may come to understand somewhat of the wisdom,
power, beneficence, and grandeur displayed in the
Divine harmony of the Universe.

"One God, one law, one element,
And one far-off Divine event
To which the whole creation moves."


Chambers's Astronomy.--Young's The Sun.-Ball's Elements of Astronomy.-
Newcomb's Popular Astronomy.-Lockyer's Spectrum Analysis.-Proctor's Other
Worlds than Ours, Saturn, The Moon, Poetry of Astronomy, &c.--Delaunay's Cours
D'Astronomie.-Haughton's Manual of Astronomy.-Newcomb and Holden's As-
tronomy.-Lockyer's Elements of Astronomy.-Norton's Spherical and Physical
Astronomy.- Herschel's Outlines of Astronomy.-Robinson's Astronomy.-M itch-
ell's Popular Astronomy. Arago's Popular Astronomy. Airy's Lectures on
Astronomy.-Hind's Solar System, and Introduction to Astronomy.-Lockyer's Ele-
mentary Lessons in Astronomy.-Proctor's Star Atlas.-Heis's Star Atlas.-Peck's
Popular Astronomy.-Gillet and Rolfe's Astronomy,--Sharpless and Phillips's As-
tronomy.-Peabody's Elements of Astronomy.-Schellen's Spectrum Analysis.--
Winchell's World-Life (excellent reading in connection with the Nebular Hypothe-
sis).-Flammarion's Wonders of the Heavens.-Guillemin's The Heavens, revised by
Proctor.-Loomis's Elements of Astronomy.-Proctor's Easy Star Lessons.-Olm-
stead's Letters on Astronomy.-Routledge's History of Science.-Buckley's History
of Natural Science.-Williamson's Problems on the Globes.-The Popular Science
Monthly (1872-1884).-Rambosson's Histoire Des Astres.


rT HIS work is designed to be recited in the topical method. On hear-
ing the title of a paragraph, the pupil should be able to draw upon
the blackboard the diagram, and to state the substance of what is con-
tained in the book. It will be noticed that the order of topics, in treat-
ing of the planets and also of the constellations, is uniform. If, each
day, a portion of the class write their topics in full upon the black-
board, it will be found a valuable exercise in spelling, punctuation,
and composition. Every point which can be illustrated in the heavens
should be shown to the class. No description or apparatus can equal
the reality in the sky. After a constellation has been traced, the pupil
should be practised in star-map drawing.
The article on "Celestial Measurements," near the close of the
work, should be constantly referred to during the term. In the figures,
and especially in the star-maps, it should be remembered that the
right-hand side represents the west ; and the left-hand, the east. To
obtain this idea correctly, the book should, in general, be held up
toward the southern sky.
For the purpose of more easily finding the heavenly bodies at any
time, Whitall's Movable Planisphere is of great service. It may be
procured of the publishers of this work. A tellurian is invaluable in
explaining Precession of the Equinoxes, Eclipses, Phases of the Moon,
etc. Messrs. A. S. Barnes & Co., New York City, furnish a good in-
strument at a low price. A small telescope, or even an opera-glass,
will be useful. A good star-map, and as many advanced works upon
Astronomy as can be secured, should be included in the teacher's


The pupil should, at the outset, get a distinct idea of the circles
and planes of the celestial sphere. The subject of angular measure-
ments can easily be made clear in this relation. A circle contains
360' ; 90 reach from horizon to zenith; 180' produce opposition;
while smaller distances can be shown in the sky (see pp. 216, 228).
Never let a pupil recite a lesson, nor answer a question, except it be
a mere definition, in the language of the booc. The text is designed to
interest and instruct the pupil ; the recitation should afford him an
opportunity of expressing what he has learned, in his own style and
Teachers desiring additional information are advised to read New-
comb's Astronomy," Young's "The Sun," Proctor's Works," Chambers's
Astronomy," and Ball's Elements of Astronomy."


INTRODUCTORY' REMARKS.............. ......... 1


HISTORY OF ASTRONOMY ............................... 5
SPACE................. .................................... 24
THE THREE SYSTEMS OF CIRCLES. ........................ 26
THE ZODIAC.. ... ................ ......................... 31

II. THE SOLAR SYSTEM............. 35

THE SUN........ ........... .................... .... 36
THE PLANETS......................................... ...... 55
VULCAN ........ ............. .. ......... ........... 71
MERCURY............... .... .......................... 71
V EN U S ........... .......... .... ..... .............. 77
THE EARTH. ............................................. 82
THE SEASONS.. ....................................... 95
PRECESSION AND NUTATION.......................... 104
THE MOON. ....... ... ............... ...........- 122
ECLIPSES..... ............................ ........... 138
THE TIDES. .......................................... 147
M ARS............................. ...................... 150
THE MINOR PLANETS ..................................... 154
JUPITER......... ............ ........... ............ 157
SATURN .............................. ................... 164
URANUS............................ ..................... 170
NEPTUNE ..... ...................... ... ............ 172


METEORS AND SHOOTING STARS................ 175
COM E TS ................................. ................ 1805
ZODIACAL LIGHT .......................................... 196


THE STARS ........................ ..................... 203
THIE CONSTELLATIONS.................................... 214
EQUATORIAL CONSTELLATIONS.................... 220
SOUTHERN CONSTELLATIONS............. ... .3........ 28
N EBUL E ....... ... ....... .. ........... ... ........ .. 246
THE MILKY W AY.... ........ ..... .. ........... 253
THE NEBULAR HYPOTHESIS............................... 255
TIM E .. ............ ................... .. ....... 263
CELESTIAL MEASUREMENTS............................. 271

IV. APPENDIX.............. .. 289

T ABLES. ... .................. ....... . . 291
QUESTIONS .................... ... .. 293
GUIDE TO THE CONSTELLATIONS .................... 313
APPARATUS ......... ................... .. 17
TELESCOPE .......................... 319
IN D EX ............. ..... ............................ ... 323


AESTRONOMY (astron, a star; nomos, a law) treats of the
Heavenly Bodies-the sun, moon, planets, stars, etc.,
and, as our globe is a planet, of the earth also. It
is, above all others, a science that cultivates the imagination.
Yet its theories and distances are based upon rigorous mathemat-
ical demonstrations. Thus the study has at once the beauty of
poetry and the exactness of Geometry.
The great dome of the sky, filled with glittering stars, is one
of the most sublime spectacles in nature. To enjoy this fully, a
night must be chosen when the air is clear, and the moon is ab-
sent. We then gaze upon a deep blue, an immense expanse
studded with stars of varied color and brilliancy. Some shine
with a vivid light, perpetually changing and twinkling; others,
more constant, beam tranquilly and softly upon us; while many
just tremble into our sight, like a wave that, struggling to reach
some far-off land, dies as it touches the shore.
In the presence of such weird and wondrous beauty, the ten-
derest sentiments of the heart are aroused. A feeling of awe and
reverence, of softened melancholy mingled with a thought of
God, comes over us, and awakens the better nature within us.
Those far-off lights seem full of meaning to us, could we but
read their message ; they become real and sentient, and, like the
soft e, es in pictures, look lovingly and inquiringly upon us. We
come into communion with another life, and the soul asserts its
immortality more strongly than ever before. We are humbled
as we gaze upon the infinity of suns, and strive to comprehend

"* This Introduction is designed merely to furnish suggestive material for conversa-
tion at the first lesson, preparatory to beginning the study. It is not intended for com-
mittal. Other topics may be found in the Questions given in the Appendix.



their enormous distances, and their magnificent retinue of worlds.
The powers of the mind are aroused, and eager questioning
crowd upon us. What are those glittering fires ? What is their
distance ? Are they worlds like our own ? Do living, thinking
beings dwell upon them ? Are they promiscuously scattered
through space, or is there a system in the universe? Can we
ever hope to fathom those mysterious depths, or are they closed
to us forever ?
Some of these problems have been solved; others yet await
the astronomer whose eye shall be keen enough to read the mys-
terious scroll of the heavens. Two hundred generations of study
have revealed to us such startling facts, that we wonder how man
in his feebleness can grasp so much, see so far, and penetrate so
deeply into the mysteries of the universe. Astronomy has meas-
ured the distance of a few stars, and of all the planets ; comn
puted the mass, size, days, years, seasons, and many physical
features of the planets; made a map of the moon; tracked
many of the comets in their immense sidereal journeys; and, at
last, analyzed the structure of the sun and stars, and announced
the very elements of which they are composed.
Observing for several evenings those stars which shine with a
clear, steady light, we notice that they change their position with
respect to the others. They are therefore called planets (literally
wanderers). Others remain immovable, and shine with a shift-
ing, twinkling light. They are termed t ihef. ': stf'rs although
it is now known that they also are in motion-the most rapid of
any known even to Astronomy---but through ,such imm11ense
orbits that they seem to us to be stationary. Then, too, diag-
onally girdling the heavens, is a whitish, vapory belt--the Mil/'ky
Way. This is composed of multitudes of millions of suns----of
which our own sun itself is one--so far removed from us that
their light mingles, and makes only a fleecy whiteness.
This magnificent panorama of the heavens is before us, inviting
our study, and waiting to make known to us the grandest revela-
tions of science.





(1. Thales.
2. Anaximander.
8. AMONG THE GRECIANS. J 3, Pythagoras.
S4. Anaxagoras & Eudoxus.
5. Hipparchus.
1. The School at Alexandria.
( 2. Ptolemy and his Theory.



SI 9. K EP LE R 'S L A W S.
; Z( 1. His Telescope.
10. GALILEO... ............ 2. His Discoveries.
(0 3. Their Reception.
Sa. Laws of Motion.
11. NEWTON, AND THE LAW b. Their Application to Moon's
l c. The Result.
(a. The Principal Circle.
1. The Hori- b, The Subord. Circle.
zon. c. Points.
d. Measurements.
STu TM P ^Q a. The Principal Circle.
2. SPACE........ TEMS OF CIR- The Equi- b The Subord. Circle.
noctial i c. Points.
CLES. d. Measurements.
(. The Principal Circle.
3. The b. The Subord. Circle,
Eclipti C. c. Points.
(d. Measurements.

Fig. .


Sir Isaac Newton.


Astronomy is the most ancient of the sciences.
The study of the stars is doubtless as old as man
himself, and hence many of its discoveries date back
of authentic records, amid the mysteries of tradition.
In tracing its history, we shall speak only of those


prominent facts that will enable us to understand its
progress and glorious achievements.
The Chinese boast much of their astronomical dis-
coveries. Indeed, their emperor claims a celestial
ancestry, and styles himself the Son of the Sun.
They possess an account of a conjunction of four
planets and the moon, which occurred in the 25th
century before Christ. They have also the first record
of an eclipse of the sun (B.C. 2128); and one of their
emperors put to death the chief astronomers Ho and
Hi for failing to announce the solar eclipse of
2169 B.C.
The Chaldeans.-The Chaldean shepherds, watch-
ing their flocks by night under a sky famed for its
clearness and brilliancy, could not fail to become
familiar with many of the movements of the heav-
enly bodies. Their priests were astronomers; and
their temples, observatories. When Alexander took
Babylon (B.C. 331), he found a record of their obser-
vations reaching back nineteen centuries.* The
Chaldeans divided the day into hours, invented the
sun-dial, and discovered the Saros, or Chaldean Pe-
riod-the length of time in which eclipses of the sun
and the moon repeat themselves in the same order.
The Grecians.-Though the Asiatics were patient
observers, they did not classify their knowledge, and
lay the basis of a science. This became the work of
the western mind.
THALES (B.C. 640-548), one of the seven sages of
"* Many astronomical inscriptions have been found in the ruins of Nineveh. In the
public library of that city there was a series of about seventy-two volumes, called the
Observations of Bel. One book treated of the polar star (then Alpha of the Dragon),
another of Venus, and a third of Mars. The earliest of these records are thought to
date back as far as 2540 B.C. (See Records of the Past, Vol. L.)


Greece, has been styled the Father of Astronomy.
He taught that the earth is round, and that the moon
receives her light from the sun. He determined
when the equinoxes and the solstices occur, and also
predicted an eclipse of the sun that is famous for
having terminated a war between the Medes and the
Lydians. These nations were engaged in a fierce
battle, but the awe produced by the darkening of the
sun was so great, that both sides threw down their
arms and made peace.
ANAXIMANDER (B.C. 610-546) invented the sun-dial,
and explained the cause of the moon's phases.
PYTHAGORAS (B.C. 570-500) founded a celebrated
astronomical school at Crotona, Italy, where were
educated hundreds of enthusiastic pupils.* He was
emphatically a dreamer. He conceived a system of
the universe, in many respects correct; yet he ad-
vanced no proof, made few converts to his views,
and they were soon well-nigh forgotten.
He held that the sun is the center of the solar sys-
tem, the planets revolving about it in circular orbits;
that the earth rotates daily on its axis, and revolves
yearly round the sun; that Venus is both morning
and evening star; that the planets are placed at
intervals corresponding to the scale in music, and
that they move in harmony, making the "music of
the spheres," but that this celestial concert is heard
only by the gods,-the ears of man being too gross
for such divine melody. He also believed that the
planets are inhabited, and he even attempted to cal-
culate the size of the animals in the moon.
"* Stp Barnes's History of the Aneient Peoples, p. 174.


ANAXAGORAS (B.C. 500-428) taught that there is but
one God, and that the sun is only a fiery globe, and
should not be worshipped. He attempted to explain
eclipses and other celestial phenomena by natural
causes, saying that there is no such thing as chance
or accident, these being only names for unknown
laws. For his audacity and impiety, as his country-
men considered it, he and his family were doomed to
perpetual banishment.
EUDoxus, who lived in the fourth century B.C., in-
vented the theory of the Crystalline Spheres. He
held that the heavenly bodies are set, like gems, in
hollow, transparent, crystal globes, which are so
pure that they do not obstruct our view, while they
all revolve around the earth; and that the planets
are placed in one globe, but have a power of moving
themselves, under the guidance-as Aristotle taught
-of a tutelary genius, who resides in each, and rules
over it as the mind rules over the body.
HIPPARCHUS, who flourished in the second century
B.C., has been called the Newton of Antiquity. He
was the most celebrated of the Greek astronomers.
He calculated the length of the year to within six min-
utes, discovered the precession of the equinoxes, and
made the first catalogue of the stars-1080 in number.
The Egyptians.-Egypt, as well as Chaldea, was
noted for its knowledge of the sciences long before
they were cultivated in Greece. It was the practice
of the Greek philosophers, before aspiring to the
rank of teacher, to travel for years through these
countries, and gather wisdom at its fountain-head.
Pythagoras spent thirty years in this kind of study.


Two hundred years after Pythagoras, the cele-
brated school of Alexandria was established.* Here
were concentrated in vast libraries and princely
halls nearly all the wisdom and learning of the
world. Here flourished the sciences and arts, under
the patronage of munificent kings.
At this school, Ptolemy (A.D. 70), a Grecian, wrote
his great work, the Almagest, which for fourteen
centuries was the text-book of astronomers. In this
work was given what is known as the Ptolemaic
System. It was founded largely upon the materials
gathered by previous astronomers, such as Hippar-
chus, whom we have already mentioned, and Era-
tosthenes, who computed the size of the earth by the
means even now considered the best-the measure-
ment of an arc of the meridian.
Ptolemaic System.-To the early astronomers, the
movements of the planets seemed extremely com-
plex. Venus, for instance, was sometimes seen as
evening star in the west, and then again as morning
star in the east. Sometimes she appeared to be
moving in the same direction as the sun, then, going
apparently behind the sun, she seemed to pass on
again in a course directly opposite. At one time,
she would recede from the sun more and more slowly
and coyly, until she would appear to be entirely sta-
tionary ; then she would retrace her steps, and seem
to meet the sun.
An attempt was made to account for all these
facts by an incongruous system of "Cycles and

See Barnes's Geleral History, p. 154.


epicycles," as it is called.* The advocates of this
theory assumed that every planet revolves in a
circle, and that the earth is the fixed center around
which the sun and the heavenly bodies move. They
then conceived that a bar, or something equivalent,
is connected at one end with the earth ; that at some
part of this bar the sun is attached; while between
that and the earth, Venus is fastened-not to the bar
directly, but to a sort of crank; and further on, Mer
cury is hitched on in the same way.
In Fig. 3, let A be the earth; S, the sun; A B D F,
the bar (real or imaginary); B C, the short bar or
crank to which Venus is tied; D E, another bar for
Mercury; F G, a fourth bar, with still another short
crank, at the end of which, H, Mars is attached.

Fig. 3.

^rl-7. 7 D-

The Ptol, j,',ic Sq.'0Il .l.

Thus they had a complete system. They did not
exactly understand the nature of these bars-
whether they were real or only imaginary-but they
did comprehend their action, as they thought; and

"* Milton refers to this when he speaks of the heavens as-
With centric and eccentric scribbled o'er,
Cycle and epicycle, orb in orb."


so they supposed the bar revolved, carrying the sun
and planets along in a large circle about the earth;
while all the short cranks kept flying around, thus
sweeping each planet through a smaller circle.
By this theory, we can see that the planets would
sometimes go in front of the sun and sometimes
behind; and their places were so accurately pre-
dicted, that the error could not be detected by the
rude instruments then in use. As soon as a new
motion of one of the heavenly bodies was discovered,
a new crank, and of course a new circle, was added
to account for the fact. Thus the system became
more and more complicated, until, at last, a com-
bination of five cranks and circles was necessary to
make the planet Mars keep pace with the Ptolemaic
theory. No wonder that Alfonso, of Castile, a
celebrated patron of Astronomy, revolted at the
cumbersome machinery, and cried out, "If I had
been consulted at the Creation, I could have done
the thing better than that."
The Saracens. After the destruction of the
library at Alexandria, learning found a home among
the Mohammedans. Bagdad on the Tigris, and Cor-
dova on the Guadalquiver became centers of
science, literature, and art. The treasures of Grecian
knowledge were eagerly gathered by the Caliphs,
and we are told that it was not uncommon to see,
entering the gates of Bagdad, a whole train of
camels loaded with Greek manuscripts. Gerbert,
afterward Pope Sylvester II., learned the elements
of astronomy at the University of Cordova, going,
after the custom of the time, to Spain for instruc-


tion, as, formerly, philosophers had gone to Egypt
In the Moorish schools, geography was already
taught by the use of the globe. The first observ-
atory in Europe was erected at
Fig Seville (1196). The fragments
of Saracenic learning that have
come down to us show that
the Arabs had constructed astro-
nomical tables, and endeavored
to perfect them by means of sys-
tematic observation of the
heavens. With the down-
fall of the Moors, and
the Revival of Learning,
Spain ceased to take the
lead in scientific study.

The iralda, Moorish Observatory at Seville.


Astrology.--During all these centuries, astronomy
owed its development quite as much to a desire of
foretelling the future, as to a love for science. It
was the prevalent belief that the stars rule the des-
tinies of men. The Chaldeans scanned the heavens
for purposes of divination, so that Chaldean and
astrologer became synonymous. Tiberius, Emperor
of Rome, practised astrology. Hippocrates himself,
the Father of Medicine (B.c. 470), ranked this among
the most important branches of knowledge for the
physician. The mysterious study possessed a pecu-
liar fascination for the Arabians, and they culti-
vated it assiduously. The Moorish astronomers were
astrologers as well, and popularized the art in west-
ern Europe. This superstition reached the height of
its influence during the Middle Ages.
The issue of any important undertaking and the
fortunes of an individual were foretold by the as-
trologer, who drew up a Horoscope representing the
position of the sun, moon, and planets at the begin-
ning of the enterprise, or at the birth of the person.
It was a complete and complicated system, and con-
tained regular rules, which guided the interpretation,
and which were so abstruse as to require years for
their mastery. Venus foretold love; Mars, war;
the Pleiades (Ple'-ya-dez), storms at sea.
The ignorant were not the only dupes of this
visionary system. Lord Bacon believed in it most
firmly. Kepler, by casting nativities, eked out his
miserable pittance as royal astronomer. So late even
as the reign of Charles II., Lilly, a famous astrolo-
ger, was called before a committee of the House of


Commons, to give his opinion on the probable issue
of some enterprise then under consideration.
However foolish the system of Astrology may
have been, it preserved the science of Astronomy
during the Dark Ages, and prompted to accurate
observation and diligent study of the heavens.
The Copernican System.-About the commence-
ment of the sixteenth century, Copernicus, breaking
away from the theory of Ptolemy, that was still
taught in the institutions of learning in Europe,
revived the theory of Pythagoras. He saw how beau-
tifully simple is the idea of considering the sun the
grand center about which revolve the earth and the
planets. He noticed how constantly, when we are
riding swiftly, we forget our own motion, and think
that the trees and fences are gliding by us in the
contrary direction. He applied this thought to the
movements of the heavenly bodies, and maintained
that, instead of all the starry host revolving about
the earth once in twenty-four hours, the earth simply
turns on its own axis, and thus produces the ap-
parent daily revolution of the sun and stars; while
the yearly motion of the earth about the sun, trans-
ferred in the same manner, would account for the
solar movements.
Though Copernicus thus simplified the Ptolemaic
theory, he yet found that the idea of circular orbits
for the planets would not explain all the phenomena,
and therefore retained the "cycles and epicycles"
Alfonso had so heartily condemned. For forty years,
this illustrious astronomer carried on his observa-
tions in the upper part of a humble, dilapidated


farm-house, through the roof of which he had an
unobstructed view of the sky. The work containing
his theory was published just in time to be laid upon
his death-bed.
Tycho Brahe, a celebrated Danish astronomer,
next propounded a modification of the Copernican
system. He rejected the idea of cycles and epicycles,
but, influenced by certain passages of Scripture,
maintained, with Ptolemy, that the earth is the
center, and that all the heavenly bodies daily re-
volve about it in circular orbits. Brahe was a noble-
man of wealth, and, in addition, received large sums
of money from the government. He erected a mag-
nificent observatory, and made many beautiful and
rare instruments. Clad in his robes of state, he
watched the heavens with the intelligence of a
philosopher and the splendor of a king. His inde-
fatigable industry and zeal resulted in the accumu-
lation of a vast fund of astronomical knowledge,
which, however, he lacked the ability to apply to any
further advance in science.
His pupil, Kepler, saw these facts, and in his fruit-
ful mind they germinated into three great truths,
called Kepler's laws. These form one of the most
precious conquests of the human mind. They are
the three arches of the bridge over which Astronomy
crossed the gulf between the Ptolemaic and Coper-
nican systems.
Kepler's Laws.-Kepler, taking the investigations
of his master, Tycho Brahe, determined to find what
is the exact shape of the orbits of the planets. He
adopted the Copernican theory-that the sun is the


center of the system. At that time, all believed the
orbits to be circular. They reasoned thus: the circle
is perfect; it is the most beautiful figure in nature;
it has neither beginning nor ending; therefore, it is
the only form worthy of God, and He must have
used it for the orbits of the worlds He has made.
Imbued with this romantic view, Kepler com-
menced with a rigorous comparison of the places of
the planet Mars as observed by Brahe, with the
places as stated by the best tables that could be com-
puted on the circular theory. For a time, they
agreed, but in certain portions of the orbit the obser-
vations of Brahe would not fit the computed place
by eight minutes of a degree. Believing that so
good an astronomer could not be mistaken as to the
facts, Kepler exclaimed, Out of these eight minutes
we will construct a new theory that will explain the
movements of all planets."
He resumed his work, and for eight years con-
tinued to imagine every conceivable hypothesis, and
then patiently to test it-" hunt it down," as he
called it. Each in turn proved false, until nineteen
had been tried. He then determined to abandon the
circle and to adopt another form. The ellipse sug-
gested itself to his mind. Let us see how this figure
is made.
Attach a thread to two pins, as at FF in the figure;
next, move a pencil along with the thread, the latter
being kept tightly stretched, and the point will mark
a curve, flattened in proportion to the length of the
string,-the longer the string, the nearer a circle
will the figure become. This figure is the ellipse.


The two points F F are called the foci (singular,
focus). We can now understand Kepler's attempt,
and the triumph which crowned his seventeen years
of unflagging toil.

Fig. .

U- _2? 0

A F -O FR_

FIRST LAw.-With this figure he constructed an
orbit having the sun at the center, and again fol-
lowed the planet Mars in its course. But very soon
there was as great a discrepancy between the ob-
served and computed places as before. Undismayed
by this failure, Kepler assumed another hypothesis,
and determined to place the sun at one of the foci
of the ellipse. Once more he "hunted down" the
theory. For a whole year he traced the planet along
the imaginary orbit, and it did not diverge. The
truth was discovered at last, and Kepler (1609) an-
nounced his first great law--
Planets revolve in ellipses, with the sun at one focus.


SECOND LAw.-Kepler knew that the planets do
not move with equal velocity in the different parts
of their orbits. He next set about establishing some
law by which this speed could be determined, and
the place of the planet computed. He drew an
ellipse, and once more marked the various positions
of the planet Mars. He soon found that when at
its perihelion (point nearest the sun) its motion
is fastest, but when at its aphelion (point furthest
from the sun) its motion is slowest. Again he
"hunted down" various hypotheses, until, at last,

he discovered that though, in going from B to A, the
planet moves more slowly, and from D to C more
rapidly, yet the space inclosed between the lines SB
and SA is equal to that inclosed between SD and SC.
Hence the second law--

A line.connecting the center of the earth with, the
center of the sun passes over equal spaces in equal
THIRD LAW.-Kepler, not satisfied with the dis-
covery of these laws, now determined to ascertain if
there were not some relation existing between the
he discovered that though, in going from B to A, the
planet moves more slowly, and from D to C more
rapidly, yet the space inclosed between the lines SB
and SA is equal to that inclosed between SD and SC.
Hence the second law--
A line.connecting the center of the earth with the
center of the sun passes over equal spaces in equal

THIRD LAW.-Kepler, not satisfied with the dis
cover of these laws, now determined to ascertain if
there were not some relation existing between the


times of the revolutions of the planets about the sun
and their distances from that body. With the same
wonderful patience, he took the figures of Tycho
Brahe, and began to compare them. He tried them
in every imaginable relation. Next he took their
squares, then he attempted their cubes. Here was
the secret; but he toiled around it, made a blunder,
and waited for months, until, once more, his patience
triumphed, and he reached (1618) the third law-
The squares of the times of revolution of the planets
about the sun are proportional to the cubes of their
mean distances from the sun.*
In rapture over the discovery of these three laws,
so marked by that Divine simplicity which pervades
all the laws of nature, Kepler exclaimed, "Nothing
holds me. The die is cast. The book is written, to
be read now or by posterity, I care not which. It
may well wait a century for a reader, since God has
waited six thousand years for an observer. f
Galileo.-Contemporary with Kepler was the great
Florentine philosopher, Galileo. He discovered the
laws of the pendulum and of falling bodies, as we
have already learned in Physics. He was, however,
educated in and believed the Ptolemaic system. A
disciple of the Copernican theory happening to come
to Pisa, where Galileo was teaching as professor in
"* For example: The square of Jupiter's period is to the square of Mars's period, as
the cube of Jupiter's distance is to the cube of Mars's distance; or, representing the
earth's time of revolution by P, and her distance from the sun by p, then letting D and
d represent the same in another planet, we have the proportion P2 : D2: : p : d3.
t Kepler, strangely enough, believed in the "Music of the Spheres." He made
Saturn and Jupiter take the bass, Mars the tenor, Earth and Venus the counter, and
Mercury the treble. This shows what a streak of folly or superstition may run through
the character of the noblest man. However, as Johnson says, a mass of metal may be
gold, though there be in it a little vein of tin.


the University, drew his attention to its simplicity
and beauty. His clear, discriminating mind per-
ceived its perfection, and he henceforth advocated it
with all the ardor of his unconquerable zeal. Soon
after, he learned that one Jansen, a Dutch watch-
maker, had invented a contrivance for making dis-
tant objects appear near. With his profound knowl-
edge of optics and philosophical instruments, Galileo
caught the idea, and soon had a telescope completed.
It was a very simple affair-only a piece of lead pipe
with a lens set at each end; but it was destined to
overthrow the old Ptolemaic theory, and revolu-
tionize the science of Astronomy.
now examined the moon. He saw her mountains and
valleys, and watched the dense shadows upon her
plains. On January 8, 1610, he turned the telescope
toward Jupiter. Near it he saw three bright stars,
as he considered them, which were invisible to the
naked eye. The next night he noticed that they had
changed their relative positions. Astonished and
perplexed, he waited three days for a fair night in
which to resume his observations. The fourth night
was favorable, and he found the three stars had
again shifted. Night after night he watched them,
discovered a fourth star, and finally found that they
were rapidly revolving around Jupiter, each in its
elliptical orbit, with its own rate of motion, and all
accompanying the planet in its journey around the
sun. Here was a miniature Copernican system, hung
up in the sky for every one to see and examine for


the most bitter opposition. Many refused to look
through the telescope lest they might become victims
of the philosopher's magic. Some prated of the
wickedness of digging out valleys in the fair face of
the moon. Others doggedly clung to the theory they
had held from their youth.* But the truth of the
Copernican system was now fully established. Phil-
osophers gradually adopted this view, and the Ptole-
maic theory became a relic of the past.
Newton, a young man of twenty-four years, was
spending the summer of 1666 in the country, on
account of the plague which prevailed at Cambridge,
his place of residence. One day, while sitting in a
garden, an apple chanced to fall to the ground near
him. Reflecting upon the strange power that causes
all bodies thus to descend to the earth, and remem-
bering that this force continues, even when we as-
cend to the tops of high mountains, the thought oc-
curred to his mind, "May not this same force extend
to a great distance out in space ? Does it not reach
the moon ?"
LAWS OF MOTION.-To understand the reasoning
that now occupied the mind of Newton, let us apply
the laws of motion as we have learned them in
"* As a specimen of the arguments adduced against the new system, the following by
Sizzi is a fair instance. There are seven windows in the head, through which the air
is admitted to the body, to enlighten, to warm, and to nourish it,-two nostrils, two
eyes, two ears, and one mouth. So in the heavens there are two favorable stars, Jupiter
and Venus; two unpropitious, Mars and Saturn; two luminaries, the Sun and Moon;
and Mercury alone, undecided and indifferent. From which, and from many other phe-
nomena in Nature, such as the seven metals, etc., we gather that the number of planets
is necessarily seven. Moreover, the satellites are invisible to the naked eye, can exercise
no influence over the earth, and would be useless, and therefore do not exist. Besides,
the week is divided into seven days, which are named from the seven planets. Now, if
we. increase the number of planets, this whole system falls to the ground,"


Physics. When a body is set in motion, it will con-
tinue to move forever in a straight line, unless
another force is applied. As there is no friction in
space, the planets do not lose any of their original
velocity, but move now with the same speed which
they received at the beginning. But this would
make them all pass along straight lines, and not cir-
cular orbits. What causes the curve ? Obviously,
another force. For example: I throw a stone into
the air. It does not move in a straight line, but in
a curve, because the earth constantly bends it down-
APPLICATION.-Just so the moon is moving around
the earth, not in a straight line, but in a curve. Can
it not be that the earth bends it downward, just as
it does the stone ? Newton knew that a stone falls
toward the earth sixteen feet the first second. He
conceived, after a careful study of Kepler's laws,
that the attraction of the earth diminishes according
to the square of the distance. He supposed (accord-
ing to the measurement then received) that a body
on the surface of the earth is exactly four thousand
miles from the center. He now applied this imag-
inary law. Suppose the body is removed four thou-
sand miles from the surface of the earth, or eight
thousand miles from the center. Then, as it is twice
as far from the center, its weight will be diminished
22, or 4 times. If it were placed 3, 4, 5, 10 times fur-
ther away, its weight would then decrease 9, 18, 25,
100 times. If, then, the stone at the surface of the
earth (four thousand miles from the center) falls
sixteen feet the first second, at eight thousand miles


it would fall only four feet; at 240,000 miles, or the
distance of the moon, it would fall only about one-
twentieth of an inch (exactly .053).
Next the question arose, "How far does the moon
fall toward the earth, i. e., bend from a straight line,
every second ?" For sixteen years, with a patience
rivaling Kepler's, this philosopher sought to solve the
problem. He toiled over interminable columns of
figures, to find how much the moon's path curves
each second. At last, he reached a result, which was
nearly, but not quite, exact. Disappointed, he laid
aside his calculations. Repeatedly he reviewed
them, but could not find a mistake. At length,
while in London, he learned of a new and more
accurate measurement of the distance from the cir-
cumference to the center of the earth. He hastened
home, inserted this new value in his calculations,
and soon found that the result would be correct.
Overpowered by the thought of the grand truth just
before him, his hand faltered, and he called upon a
friend to complete the computation.
From the moon, Newton passed on to the other'
heavenly bodies, calculating and testing their orbits.
Finally, he turned his attention to the sun, and, by
reasoning equally conclusive, proved that the attrac-
tion of that great central orb compels all the planets
to revolve about it in elliptical orbits, and holds them
with an irresistible power in their appointed paths.*

Do not understand me at all as saying there is no mystery about the planets' mo-
tion. There is just one single mystery,-gravitation; and it is a very profound one.
How it is that an atom of matter can attract another atom, no matter how great the
distance, no matter what intervening substance there may be; how it will act upon
it, or at least behave as if it acted upon it,-I do not know, I cannot tell. Whether they


At last, he announced this grand Law of Gravita-
tion: Every particle of matter in the universe at-
tracts every other particle of matter with a force
directly proportional to its quantity of matter, and
decreasing as the square of the distance increases.

WE now in imagination pass into space, which
stretches out in every direction, without bounds or
measures. We look up to the heavens, and try to
locate some object among the mazes of the stars.
Bewildered, we feel the necessity of some system of
measurement. Let us try to understand the one
adopted by astronomers.
The Celestial Sphere.-The blue arch of the sky,
as it appears to be spread over us, is termed the
Celestial Sphere. There are two points to be noticed
First, that so far distant is this imaginary arch
from us, that if any two parallel lines from different
parts of the earth were drawn to this Sphere, they
would apparently intersect. Of course, this could
not be the fact; but the distance is so immense, that
we are unable to distinguish the little difference of
are pushed together by means of an intervening ether, or what is the action, I cannot
understand. It stands with me along with the fact, that, when I will my arm to rise, it
rises. It is inscrutable. All the explanations that have been given of it seem to me
merely to darken counsel with words and no understanding. They do not remove the
difficulty at all. If I were to say what I really believe, it would be, that the motion of
the spheres of the material universe stand in some such relation to Him in whom all
things exist, the ever-present and omnipotent God, as the motions of my body do to my
will : I do not know how, and never expect to know."-Prof. Young.


four or even eight thousand miles, and the two lines
would seem to unite: so we must consider this great
earth as a mere speck or point at the center of the
Celestial Sphere.
Second, that we must neglect the entire diameter
of the earth's orbit, so that if we should draw two
parallel lines, one from each end of the earth's orbit,
to the Celestial Sphere, although these lines would
be nearly 186,000,000 miles apart, yet they would
appear to pierce the Sphere at the same point; which
is to say, that, at that enormous distance, 186,000,000
miles shrink to a point. Consequently, in all parts
of the earth, and in every part of the earth's orbit,
we see the fixed stars in the same place.
This sphere of stars surrounds the earth on every
side. In the daytime, we cannot see the stars be-
cause of the superior light of the sun ; but, with a
telescope, they can be traced, and an astronomer will
find certain stars as well at noon as at midnight.
One half of the sphere is constantly visible to us;
and so far distant are the stars, that we see just as
much of the sphere as we should if the upper part of
the earth were removed, and we were to stand four
thousand miles further away, or at the center of the
earth, where our view would be bounded by a great
circle of the earth.
On the concave surface of the Celestial Sphere,
there are imagined to be drawn three systems of
circles: the HORIZON, the EQUINOCTIAL, and the
ECLIPTIC SYSTEM. Each of these has (1) its Prin-
cipal Circle, (2) its Subordinate Circles, (3) its
Points, and (4) its Measurements.


(a) The Principal Circle is the Rational Horizon.
This is the great circle whose plane, passing through
the center of the earth, separates the visible from the
invisible heavens. The Sensible Horizon is the small
circle where the earth and the sky seem to meet: it
is parallel to the rational horizon, but distant from
it the semi-diameter of the earth. No two places
have the same sensible horizon : any two, on opposite
sides of the earth, have the same rational horizon.
Fg. (b) The Subordinate Cir-
z *cles are the Prime Verti-
cal circle, and the Merid-
^ :, wian. A vertical circle is
one passing through the
/ poles of the horizon (ze-
-H I-1 nith, and nadir). The
Prime Vertical is a verti-
cal circle passing through
""p' the East and West points
The M eridian is a vertical
circle passing through the
E, center of earth ; Z, zenith; Z', nadir ;
PP', axis of earth; HAH', horizon; S, a North and South points.
star; ZSZ', vertical circle passing through
S; AS, altitude ofstar; ZS, zenith distance (c) The Points are the
of star; H'A, azimuth of star.
Zenith, the Nadir, and the
N., S., E., and W. points. The Zenith is the point
directly overhead, and the Nadir, the one directly
underfoot. They are also the poles of the horizon--
i. e., the points where the axis of the horizon pierces
the Celestial Sphere. The N., S., E., and W. points
are familiar.


(d) The Measurements are Azimuth, Amplitude,
Altitude, and Zenith distance.
AZIMUTH is the distance from the meridian, meas-
ured east or west, on the horizon, to a vertical circle
passing through the object.
AMPLITUDE (the complement of Azimuth) is the
distance from the Prime Vertical, measured on the
horizon, north or south.
ALTITUDE is the distance from the horizon, meas-
ured on a vertical circle, toward the zenith.
ZENITH DISTANCE (the complement of Altitude) is
the distance from the zenith, measured on a vertical
circle, toward the horizon.
The Horizon system is one commonly used in
observations with Mural Circles, and Transit Instru-


(a) The Principal Circle is the Equinoctial. This
is the Celestial Equator, or the earth's equator ex-
tended to the Celestial Sphere. At all places between
the equator and the pole, the celestial equator is in-
clined to the horizon at an angle equal to the dis-
tance of the zenith of the place from the pole.*
(b) The Subordinate Circles are the Hour Circles
(Right Ascension Meridians), the Colures, and the
Declination Parallels.
The latitude of a place is its distance from the equator, and this equals the distance
of the zenith of the place from the equinoctial. Hence, having given the latitude of a
place, to find the height of the celestial equator above its horizon, subtract the latitude
from 900, and the remainder is the required angular distance. In like manner, the lati-
tude subtracted from 900 gives the co-latitude of the place-the complement of th1


THE HOUR CIRCLES are thus located. The Equi-
noctial is divided into 360, equal to twenty-four
hours of motion-thus making 15 equal to one hour
of motion. Through these divisions run twenty-four
meridians, each constituting an hour of motion
(time) or 15 of space. The Hour Circles may be
conceived as meridians of terrestrial longitude (15
apart) extended to the Celestial Sphere.
THE COLURES are two principal meridians; the
Equinoctial Colure is the meridian passing through
the equinoxes; the Solstitial' Colure is the meridian
passing through the solstitial points.
parallel to the Equinoctial; or they may be conceived
as the parallels of terrestrial latitude extended to the
Celestial Sphere.
(c) The Points are the Celestial Poles, and the
THE CELESTIAL POLES are the points where the
axis of the earth extended pierces the Celestial
Sphere, and are the extremities of the celestial axis,
as the poles of the earth are the extremities of the
earth's axis. The North Pole is marked very nearly
by the North Star, and every direction from that is
reckoned south, and every direction toward that is
reckoned north, however it may conflict with our
ideas of the points of the compass.
THE EQUINOXES are the points where the Equinoc-
tial and the Ecliptic (the sun's apparent path through
the heavens) intersect.
(d) The Measurements are Right Ascension (R.A.),
Declination, and Polar Distance.


RIGHT ASCENSION is distance from the Vernal
Equinox, measured on the equinoctial eastward
to the meridian which passes through the body.
R. A. corresponds to terrestrial longitude, and may
extend to 3600 East, instead of 1800 as on the earth.
R. A. is never measured westward. The starting
point is the meridian passing through the vernal
equinox, as the meridian passing through Green-
wich is the point from which terrestrial longitude is
DECLINATION is distance from the equinoctial,
measured on any Hour Circle or meridian north or
south. It corresponds to terrestrial latitude.
POLAR DISTANCE (the complement of Declination)
is the distance from either Pole, measured on an
Hour Circle.
The Equinoctial System is largely used by modern
astronomers, and accompanies the Equatorial Tele-
scope, Sidereal Clock, and Chronographs of the best

(a) The Principal Circle is the Ecliptic. This is
the apparent path of the sun in the heavens. It is
inclined to the equinoctial 23" (23' 27' 15", Jan. 1,
1884), which measures the inclination of the Earth's
Equator to its orbit, and is called the obliquity of the
ecliptic. (See p. 58.)
The inclination of the ecliptic to the horizon, unlike
that of the equinoctial, varies at different times of
the year. The angle that the ecliptic makes with
the horizon is greatest when the vernal equinox is


on the western horizon and the autumnal on the
eastern; it is least when the vernal equinox is on
the eastern horizon and the autumnal on the western. *
(b) The Subordinate Circles are Circles of Celestial
Longitude, and Parallels of Celestial Latitude.
seldom employed. They are measured on the Eclip-
tic, as circles of Right Ascension (R. A.) are meas-
ured on the Equinoctial.
used. They are small circles drawn parallel to the
ecliptic, as parallels of declination are drawn parallel
to the equinoctial.
(c) The Points are the Poles of the Ecliptic, the
Equinoxes, and the Solstices.
THE POLES OF THE ECLIPTIC are the points where the
axis of the earth's orbit meets the Celestial Sphere.
THE EQUINOXES are the points where the ecliptic
intersects the equinoctial. The place where the sun
crosses the equinoctial f in going north, which occurs
about the 21st of March, is called the Vernal Equinox.
The place where the sun crosses the equinoctial in
going south, which occurs about the 21st of Septem-
ber, is called the Autumnal Equinox. The Solstices
are the two points of the ecliptic most distant from
the Equator; or they may be considered to mark the
sun's furthest declination north and south of the
equinoctial. The Summer Solstice occurs about the
In the former instance, the angle is equal to the co-latitude, plus 231 (the inclina-
tion of the ecliptic to the equinoctial); and, in the latter, the co-latitude minus 234 .
Thus, at the latitude of New York, it varies from 90 41" + 2310 = 724 0 ; to 90-
410 231 = 251'. In the one case, the summer solstice is on the meridian of the
place, and, in the other, the winter.
+ This is commonly called crossing the line.' "


21st of June; the Winter Solstice occurs about the
21st of December.
(d) The Mleasurements are Celestial Longitude and
CELESTIAL LONGITUDE iS distance from the Vernal
Equinox measured on the ecliptic, eastward.
CELESTIAL LATITUDE is distance from the ecliptic
measured on a Subordinate Circle, north or south.
A belt of the Celestial Sphere, 8 on each side of
the ecliptic, is styled the Zodiac. This is of very
high antiquity, having been in use among the
ancient Hindoos and Egyptians. The Zodiac is
divided into twelve equal parts-of 30 each-called
Signs, to each of which a fanciful name is given.
The following are the names of the

A ries.................. ... Libra. ... ...... ....
Taurus..... ........... y Scorpio ................ 111
Gemini .. ......... .. T Sagittarius .... ........
Cancer ................. Capricornus ............
Leo .................. 5. Aquarius ..............
Virgo. ................. TI Pisces ............... .
"The first, I, indicates the horns of the Ram; the
second, the head and horns of the Bull; the barb
attached to a sort of letter, n, designates the Scor-
pion; the arrow, I, sufficiently points to Sagitta-
rius; v is formed from the Greek letters, rp, the two
first letters of rpa)yo, a goat. Finally, a balance,
the flowing of water, and two fishes, tied by a string,
may be imagined in u, and X, the signs of Libra,
Aquarius, and Pisces." (See pp. 210, 295.)



1. How high is the North Star above your horizon ?
2. What is the sun's right ascension at the autumnal equinox? At the
vernal equinox ?
3. What was the first discovery made by the telescope ?
4. How high above the horizon of any place are the equinoctial points
when they pass the meridian ?
5. Jupiter revolves around the sun in 12 of our years. Assuming the
earth's distance from the sun to be 93,000,000 miles, compute Jupiter's dis-
tance by applying Kepler's third law.
6. The latitude of Albany is 42' 39' N; what is the sun's meridian
altitude at that place when it is in the celestial equator ?
7. What is the co-latitude of a place ?
8. What is the declination of the zenith of the place in which you
reside ?
9. Why are the stars generally invisible by day ?
10. Why is the ecliptic so called ?
11. Who first taught that the earth is round ?
12. What is Astrology ?
13. How can we distinguish the fixed stars from the planets ?
14. How long was the Ptolemaic System accepted ?
15. In what respect did the Copernican System differ from the one now
received ?
16. For what is Astronomy indebted to Galileo ? To Newton ?
17. What is the amount of the obliquity of the ecliptic ?
18. Define Zenith. Nadir. Azimuth. Altitude. Equinoctial. Right
Ascension. Declination. Equinox. Ecliptic. Colure. Solstice. Polar
distance. Zenith distance. The Zodiac.
19. If the R. A. of the sun be 80', state in what sign ihe is then located ?
1600 ? 2800
20. Why does the angle which the ecliptic makes with the horizon vary ?
21. Why is the angle which the celestial equator makes with the horizon
constant ?



"In them hath He set a tabernacle for the sun."
This world was once a fluid haze of light,
Till toward the center set the starry tides
And eddied into suns, that wheeling cast
The planets."-TENNYSON.

S1. D TSTA NCE x a D iscov ery .
2. LIGHT & HEAT. Number and Location.
c. Size.
3. APPARENT SIZE. d. Constituents.
4. REAL DIIEN- e. Motion across Disk.
f. Change in Rate.
g. Prove the Rotation of Sun.
h. Synodic and Sidereal Rotation
5. SOLAR SPOTS... i. Path of Spots.
S. Individual Motion.
I. THE SUN. ... k. Change in Form.
1. Periodicity of Spots.
m. Planetary Influence.
n. Influence on Terrestrial Heat, etc.
o. Heat of Spots.
p. Depression of Spots.
q. Brightness of Spots.
r. Faculae, rice-grains, etc.
6. PHYSICAL CON- a. Wilson's Theory.
STITUTION.. .. ..) b. Present Theory (Kirchhoff's).
a. Common Characteristics.
b. Comparison of Planets.
c. Properties of the Ellipse.
-INTRODUCTmION. d. Planetary Orbits.
e. Comparative Size of Planets.
f. Conjunction of.
g. Are Planets Inhabited ?
1. V LCAN. to p. Division of Planets, etc.
S1. V U LCA N .
a. Description.
H b. Motion in Space.
S2. MERCU. c. Distance from Earth.
^~~ ~2. MERCURY .... .. Dimensions.
d. Dimensions.
)j e. Seasons.
f. Telescopic Features.
3 8. VENUS ....... .. .. .Repeat same Analysis as of Mercury.
( a. Dimensions.
b. Rotundity.
O c. Apparent & Real Motion.
( 1. Diurnal Moo
tion of Sun.
W 2. Unequal rate
of Motion.
d. Diurn'Mo- of Motion.
SII THE PLANETS. Diu l Mo- 3. Orbits of
E4. THE EARTH................. tion o. Stars.
4. Unequal Ve-
Sa. Motion. locities ofStars.
b. Dimens'ns. 5. Appearance
c. Librations. of Stars, etc.
d. L'g't &H't. 1. Change inl
e. Cen.ofGrav. appearance of
f. Atmosphere. heavens.
g. Lunarians. c rly 2. Yearly path
tion of
MoN h. Earth-shine. on o of Sun.
-THE MOON. p Sun : its <
i. Phases. Sun : its 3. Moves N.& S.
j. Harv'stIM'n. Conse- 4. Change of
-ECLIPSES. k. Wet Moon. quences. Seasons, etc. 20
1. Nodes. points under
m. Occulat'n. this topic.
--THE TIDES. n. Seasons. f. Precession of Equinoxes.
o. Telescopic g. Nutation.
Features. h. Refraction & Aberration,
i. Parallax.
5. MARS.........Same Analysis as Mercury.
7. JUPITER...... Same Analysis as Mercury.
8. SATURN.. ....
9. URANUS......
10. NEPTUNE. ..
III, METEORS, AND SHOOTING STARS ) The subjects of the paragraphs may be inserted
IV. COMETS .. .. .. .. .. .. .. ... by tle pupil, to complete these analyses, at
V. THE ZODIACAL LioHT ........ ) th' pleasure of the teacher.



T HE Solar System is mainly comprised within
the limits of the Zodiac. It consists of-

1. The Sun-the center.
2. The major planets-Vulcan (undetermined), Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
3. The minor planets, at present (1884) two hundred and thirty-
seven in number.
4. The satellites, or moons, twenty in number, which revolve around
the different planets.
5. Meteors and shooting-stars.
6. Thirteen comets, which have now been found, by a second re-
turn, to move, like the planets, in elliptic paths, and to
revisit the sun periodically.
7. The Zodiacal Light.

How we are to imagine the solar system to our-
selves.-We are to think of it as suspended in space;
being held up, not by any visible object, but in
accordance with the law of Universal Gravitation
discovered by Newton, whereby each planet attracts
every other planet and is in turn attracted by all.
First, the Sun, a great central globe, so vast as to
overcome the attraction of all the planets, and com-
pel them to circle around him; next, the planets,


each turning on its axis while it flies around the sun
in an elliptical orbit; then, accompanying these, the
satellites, each revolving about its own planet, While
all whirl in a dizzy waltz about the central orb;
next, the comets, rushing across the planetary
orbits at irregular intervals of time and space; and
finally, shooting-stars and meteors darting hither
and thither, interweaving all in apparently inex-
tricable confusion.
To make the picture more wonderful still, every
member is flying with an inconceivable velocity, and
yet with such accuracy that the solar system is the
most perfect timepiece known.


Sign, O, a buckler with its boss.

Distance.-The sun's average distance from the
earth is nearly 93,000,000 miles. Since the earth's
orbit is elliptical, and the sun is situated at one of its
foci, the earth is 3,000,000 miles further from the sun
"in aphelion than in perihelion.
"* The sun's distance from the earth is determined, as we shall learn hereafter (see
Celestial Measurements), by means of the solar parallax. In the former editions of this
work, the parallax of 8".94-deduced principally from observations upon the planet Mars
in 1862-was accepted. This gave a solar distance of about 911 million miles, and has
been in general use among astronomers until recently. The observations of the last few
years have, however, shown that the true parallax is smaller, and that the sun is a
little further off than was supposed. Astronomers are not fully agreed upon the exact
parallax that should be adopted, but there seems to be a general converging of opinion
toward 8".80 as being, if not the exact parallax, at least as near it as we are able at
present to come. This new determination of the solar parallax renders necessary a cor-
responding change in the planetary distances, etc., as the sun's distance is the unit used
by astronomers in making all celestial measurements. In this chapter, the author has
followed the data given by Prof. Young in his work upon the Sun, as being the most
recent and authoritative view. (See p. 2,0.)


As we attempt to locate the heavenly bodies in
space, we are startled by the enormous figures em-
ployed. The first number, 93,000,000 miles, is far
beyond our grasp. Let us, however, try to compre-
hend it.* If there were air to convey a sound from
the sun to the earth, and a noise could be made loud
enough to pass that distance, it would require over
fourteen years for it to come to us. Suppose a rail-
road could be built to the sun. An express-train,
traveling day and night, at the rate of thirty miles
an hour, would require 352 years to reach its destina-
tion. Ten generations would be born and would die;
the young men would become gray-haired, and their
great-grandchildren would forget the story of the
beginning of that wonderful journey, and would
read it in history, as we now read of Queen Elizabeth
or of Shakspere; the eleventh generation* would
see the solar station at the end of the route. Yet
this enormous distance of 93,000,000 miles is used as
the unit for expressing celestial distances,-as the
foot-rule for measuring space; and astronomers
speak of so many times the sun's distance as we
speak of so many feet or inches.
The Light of the Sun is equal to 5,563 wax-candles
held at a distance of one foot from the eye. It
would require 600,000 full-moons to produce a day as
brilliant as one of cloudless sunshine. t
"* If a babe were born with an arm long enough to reach the sun, and should touch
that fiery globe, the infant would grow to manhood and to old age and finally die, before
the sensation could traverse the nerve to his brain, and he feel the burn.
t According to Langley, the sun is blue, and to the inhabitants of other worlds may
shine as a bluer star than Vega. The light from different parts of the solar disk, how-
ever, varies in color: while that from the center has a tint, that from the
edge is of a chocolate hue. This difference is probably owing to the fact that the latter


The Heat of the Sun.-The amount of heat we
receive annually is sufficient to melt a layer of ice
110 feet thick, extending over the whole earth.* Yet
the sunbeam is only -& W,o part as intense as it is at
the surface of the sun. Moreover, the heat and light
stream off into space equally in every direction. Of
this vast flood, only one twenty-three-hundred-
millionth part reaches the earth.
If the heat of the sun were produced by the burn-
ing of coal, it would require a layer sixteen feet in
thickness, extending over its whole surface, to feed
the flame a single hour. Were the sun a solid body
of coal, it would burn up at this rate in forty-six
centuries. "Sir John Herschel says that if a solid
cylinder of ice 45 miles in diameter and 200,000 miles
long were plunged, end first, into the sun, it would
melt in a second of time.
Apparent Size.-The sun appears to be a little over
half a degree in diameter, so that 337 solar disks,
laid side by side, would make a half-circle of the
celestial sphere. It seems a trifle larger to us in
winter than in summer, as we are 3,000,000 miles
nearer it. If we represent the luminous surface of
the sun when at its average (mean) distance by 1,000,
the same surface will be represented when in aphe-
lion (July) by 967, and when in perihelion (January)
by 1,034,

passes through a greater thickness of the solar atmosphere, while our own atmosphere
does its part in strangling the blue rays of the sunlight, the red rays filtering through
with little loss.
Recent experiments by Langley seem to increase this estiniea t that of a sheet
of ice 180 feet thick (Popular ceiec ie Monthly, 8ept, 18s-.)

THE -SUN. 39

Dimensions.-Its diameter is about 866,000 miles.*
Let us try to understand this amount by comparison.
A mountain upon the surface of the sun, to bear
the same proportion to the globe itself as the loftiest
peak of the Himalayas does to the earth, would need
to be about 600 miles high.
Again: Suppose the sun were hollow, and the
earth, as in the cut (Fig. 8), placed at the center, not

Fig. 8.

/ \

I 0
/ N
\ 1t

\B -- '- /O

only would there be room for the moon to revolve in
its regular orbit within the shell, but that. would

Pythagoras, whose theory of the universe was in so many respects very like the
one we receive, believed the sun to be 44,000 miles from the earth, and seventy-five
'miles in diameter.


stretch off in every direction nearly 200,000 miles
Its volume is 1,300,000 times that of the earth-
i. e., it would take 1,300,000 earths to make a globe
the size of the sun. Its mass is 750 times that of
all the planets and moons in the solar system, and
330,000 times that of the earth. Its weight may be
expressed in tons, thus:


The Density of the sun is only about one-fourth
that of the earth, or 1.41 that of water, so that the
weight of a body transferred from the earth to the
sun would not be increased in proportion to the com-
parative size of the two. On account also of the vast
size of the sun, its surface is so far from its center
that the attraction is largely diminished, since that
decreases, we remember, as the square of the dis-
tance. However, a man weighing at the earth's
equator 150 lbs., at the sun's equator would weigh
about two tons,-a force of attraction that would in-
stantly crush him. At the earth's equator, a stone
falls 16 feet the first second; at the sun's equator, it
would fall 444 feet. t
Telescopic Appearance of the Sun: Sun Spots.-
We may sometimes examine the sun at early morn-
ing or late in the afternoon with the naked eye, and

This number is meaningless to our imagination, but yet it represents a force of
attraction that holds our own earth and all the planets steadily in their places; while it
fills the mind with an indescribable awe as we think of that Being who made the sun,
and holds it in the very palm of His hand."
t A singular consequence of this has been suggested. "A cannon-ball could be
thrown only a short distance, since it would pass through a path of great curvature, and
would fall to the sun within a few yards of the gun."


at. midday by using a smoked glass. The disk will
appear distinct and circular, and with no spot to dim
its brightness. If we use a telescope of moderate

Fig. 9.

ii .r:: ...... .' ,4,,l

.P ,..

-2 "' PI'



power, taking the precaution to shield the eye with
a colored eye-piece, we shall find the surface of the
sun sprinkled with irregular spots (Fig. 9).*

The natural purity of the sun seems to have been formerly an article of faith among
astronomers, and therefore on no account to be called in question. Scheiner, it .is said,
having reported to his superior that he had seen spots on the sun's face, was abruptly
dismissed with these remarks : I have read Aristotle's writings from end to end many
times, and I assure you I do not find anything in them similar to that which you men-
tion. Go, my son, tranquillize yourself ; be assured that what you take for spots are the
faults of your glasses or your own eyes."


seem to have been noticed as early as 807 A.D., al-
though the telescope was not invented until 1610,
and Galileo is considered to have discovered them in
the following year.*
NUMBER AND LocATION.-Sometimes, but rarely,
the sun's disk is clear. During a period of ten years,
observations were made on 1982 days, on 372 of
which there were no spots seen. As many as two
hundred spots have been noticed at one time. They
are mostly found in two belts, one on each side of
the equator, within not less than 100 nor more than
30' of latitude. They seem to herd together,-the
length of the straggling group being generally par-
allel to the equator.
SIZE OF THE SPOTS.-It is not uncommon to find a
spot with a surface larger than that of the earth.
Schroter measured one more than 29,000 miles in
diameter. Sir J. W. Herschel calculated that one
which he saw was 50,000 miles in diameter. In
1843, one was seen which was 75,000 miles across,
and was visible to the naked eye for an entire week. t
On the day of the eclipse in 1858, a spot over 108,000
miles broad was distinctly seen, and attracted gen-
eral attention in this country. In 1839, Captain Davis
saw one which he computed was 180,000 miles long,
and had an area of twenty-four billion square miles.
If these are deep openings in the luminous atmos-
"* We read in the log-book of the good ship Richard of Arundell, on a voyage, in
1590, to the coast of Guinea, that on the 7, at the going down of the sunne, we saw a
wreat black spot in the sunne ; and the 8 day, both at rising and setting, we saw the like,
-which spot to me seeming was about the bignesse of a shilling, being in 5 degrees of
ititude, and still there came a great billow out of the souther board."
t 1f on the sun's surface 450.3 miles. This spot was 2'47" across (Schwabe).


phere of the sun, what an abyss must that be at the
bottom of which our earth could lie like a boulder in
the crater of.a volcano!"
companying repre-
sentation, it will be Fi. 10,
seen that the spots I
generally consist
of one or more dark
portions called the
umbra, and around
that a grayish por-
tion styled the pe-
numbra (pene, al-
most, and umbra,
black). Sometimes,
however, umbrae
appear without a Sun-Spots.
penumbra, and vice
versa. The umbra itself has generally a dense black
center, called the nucleus. Besides this, the umbra
is sometimes divided by luminous bridges.
SPOTS ARE IN MOTION.-The spots change from day
to day; but all have a common movement. About
fourteen days are required for a spot to pass across
the disk of the sun from the eastern side, or limb, to
the western; in fourteen days, it reappears, changed
in form perhaps, but generally recognizable.
the eastern limb; day by day it progresses, with a
gradually-increasing rapidity, until it reaches the


center; it then slowly loses its rapidity, and finally
disappears on the western limb. The diagram illus-
trates the apparent change which takes place in the
form. Suppose at first the spot is of an oval shape;
as it approaches the center it apparently widens and
becomes circular. Having passed that point, it be-
comes more and more oval until it disappears.

Fig. 11.

..... ............... ...... ........ ......
------ ----- -.4J.........

Change in Spots as they Cross the Dicsk.

TION ON ITS Axis.-These changes can be accounted
for only on the supposition that the sun rotates on
its axis: indeed, they are the precise effects which
the laws of perspective demand in that case. About
twenty-seven days elapse from the appearance of a
spot on the eastern limb before it is seen a second
time. During this period the earth has gone forward
in its orbit, so that the location of the observer is
changed; allowing for this, the sun's time of rotation
at the equator is about twenty-five days (25 d., 8 h.,
10 m.: LanCier),


Curiously enough, the equatorial regions move
more rapidly, and complete a rotation in less time,
than the rest of the sun. While a spot near the
equator performs a rotation in twenty-seven days,
one situated half- Fg. 2.
Fig. 12.
way to either pole, ,
requires nearly
twenty-eight days.
can easily under-
stand why we make
an allowance for
the motion of the
earth in its orbit.
Suppose a solar spot
at a, on a line pass-
ing from the center
of the earth to the
center of the sun. \T
For the spot to pass
around the sun and --
come into that same Synodic and Sidereal Revolutions.
position again, requires about twenty-seven days.
But, during this time, the earth has passed on from
T to T'. The spot has not only traveled around to
a again, but also beyond that to a', or the distance
from a to a' more than an entire revolution. To do
this, requires about two days. A revolution from a
around to a' is called a synodic, and one from a
around to a again is called a sidereal, revolution.


Sometimes their path curves toward the north, and

Fig. 13.

March. June. September.

sometimes toward the south, as in the figure. This
can be explained only on the supposition that the
sun's axis is inclined to the ecliptic (7 15').
motion already named as assigned to the sun's rota-
tion, nearly every spot seems to have an individual
motion. Some spots circle about in small elliptical
paths, often quite regularly for weeks and even
months. Immense cyclones occasionally pass over
the surface with fearful rapidity, producing rotation
and sudden changes in the spots. At other times,
however, the spots seem "to set sail and move
across the disk of the sun like gondolas over a silver
and then disappear under the eye of the astronomer.
Wollaston saw one that seemed to be shattered like
a fragment of ice when it is thrown on a frozen
surface, breaking into pieces, and sliding off in
every direction. Sometimes one divides itself into
several nuclei, while again several nuclei coirn ne


into a single nucleus. Occasionally a spot will re-
main for six or eight rotations, while often it will
last scarcely half an hour. Sir W. Herschel relates

Fig. 14.

S..... *--..-"

Solar Cyclone, May 5th, 1857. (Secchi.)
i -u

Solar Cyclone, May 5th, 1857. (Secchi.)

that, when examining a spot through his telescope,
he turned away for a moment, and on looking back
it was gone.
a remarkable fact that the number of spots increases
and diminishes through a regular interval of about
11.11 years. These periodic variations are closely
connected with similar variations in the aurora
and magnetic earth-currents which interfere with
the telegraph.

"* The regular increase and diminution in the number of the spots was discovered
by Schwabe of Prussia, who watched the sun so carefully that it is said "for thirty years
the sun never appeared above the horizon without being confronted by his imperturbable


Many astronomers of high standing believe that the
solar spots are especially sensitive to the approach
of Mercury and Venus, on account of their nearness,
and of Jupiter, because of its size; that the area of
the spots exposed to view from the earth is uniformly
greatest when any two of the larger planets come
into line with the sun; and that when both Venus
and Jupiter are on the side of the sun opposite to us,
the spots are much larger than when Venus alone is
in that position. Most authorities, however, doubt
the accuracy of these observations, and deny this
planetary influence altogether.
SEASON.-Herschel first advanced the idea that years
of abundant spots would be years also of plentiful
harvest. This is not now generally received. What
two years could be more dissimilar than 1859 and
1860 ? Both abounded in solar spots, yet, in Europe,
one was a fruitful year and the other one of almost
famine. Whether the spots influence the weather is
still a mooted question.
FACE.-It seems that the breaking out of a spot sen-
sibly diminishes the temperature of that portion of
the sun's disk. The facule, on the other hand, do
not increase the temperature (Secchi).
SPOTS ARE DEPRESSIONS. Careful observations
show that, in general, the "floor," so to speak, of the
umbra is sunk from two to six thousand miles below
the level of the luminous surface (Young).
If we represent the ordinary brightness of the


Fig. 15.

S : ^ -' .... '. "' '.'. i .
:. .. .. .

ley). There may be

radiated by a spot, ,...."""" "" """ "^"":"\-'"".
sun compared the sn that of the penumbra wo

f ley. There may be

even a calcium light.:, .:
held between our eyes
and the sun, appears '
as a black spot on the
disk of that luminary,
telescope of moderate
power will show the "",m .
surface of the sun to have a peculiar mottled appear-
leg).Theremay b
much: lih an het 6

surface of the sun to have a peculiar mzottledl appear-


ance not unlike that of an orange skin. But, under
favorable circumstances and with a telescope of high
power, the solar disk is found to be covered with
small, intensely bright bodies irregularly distributed.

Fig. 17.
;":: ^:'.?*::- i' : ^'..." :: ', .,,, "- "1 : C ". ".


These are now known as rice-grains.* They are
often apparently crowded together in luminous
ridges, or streaks, termed faculce .(facula, a torch) ;
while the rice-grains themselves, according to Prof.
', .',; ,

Langley, are composed of granules. Minute as a

Various observers describe the solar surface differently. A peculiar, elongated,
leaf-shaped appearance of the rice-grains, called the willow-leaf structure, is shown in
I.... :-

Fig. 17, as seen by Nasmyth. Newcomb compares the sun's appearance to that of a
plate of rice-soup. Young says it frequently resembles bits of straw lying parallel to
one another--the thatched-straw formation."
L .. ..
F ,.',;,,,, '. ,

,, .. .-...'.'.. "- ..
S.. ..... ..
W'".. "w L.e

Te a nw oa:s rice grains They :ar e ..

i in, cLed th w e i

'i jjj*~irw;yg"fi ""~V~'~i~if~Pt
\%,.. c'\'v v 'I I" __ f~ill 11111,, ir I ii i 1f11f ~t% .
\y, ~ ~~~11; i g,. T, Mvff4I% 11 "11 I Iff ,~ iI~ 9 4 & o~
IA'" go ,,IJ W Y.

"A "' R.

'R A Jill '"" .

X "X..- Ml "
A... .

-- --- _C' .,"- _, ,- ",
gs~~.~T '"I -. ,k .4\.: ii .,4 ">

----' _ -. .N '
--- -.

zz ./., 1/
As,/ .

n N.R: R/a

& .31.,, .', W 11 11"
n.a..,.. ,-M -,:lpo n

"ftN -A',.. /!.'\'

c" '. ;,
Z'P\N 7 \40 V II

N I /,,, .,,

'I ..N "Q.N '
.. : ,,,' ~
'..3 11b A14%~

.., ,.
Ni _./"r V. ,,` "
-'/ If''" N
R xv~

,M. '/.
2M Or

gm: W ,,


Ix$% '.,

:r .
P,--.,- --\ s '- #-M,.1

$iT4'V ''p/'k'ca ,/iQ u-sot o w
OR k

\\A4 \% 4'. N>

'r 'N V ." \: \
-:~\ %\\.qM
/A101 1W~~1

-~~~~. N~t -. ~

*"''' Yn SL'
y Sum-pot :of ce
I ,. ~ : B"\Ro
~~, --~ 2~RN -x
X 3"Ri -~'
'I ~ W

Pill. V IL
0j. "VA:.
":~e wI!' N
,: /,, `~z ; ZU
-7 A.- Na\N1_1 !I
11. Z/ 1 Y; 100"

1 0 1.I
''~N RT i 1
N 0/7
j.. &L
I, fit :jilli".1!
~ ii,.-~~~i~,,ow~
'I 5t
c ~r ;':4
R, S \OtN 11 ON
17. 1 t &
11 1 jPljV WIAk -AR
i ;l :t_ __ zLEK 2z -

'0 `I i'' ill, ilk
xv U qt
A, 1 15

A, i v A afDC./y7!sown he~aret pitngt tecntr


granule seems, probably the smallest has a diameter
of, at least, 100 miles.
Physical Constitution of the Sun.*-Of the consti-
tution of the sun, and the cause of the solar spots,
very little is definitely known.
WILSON'S THEORY supposed that the sun is com-
posed of a solid, dark globe, surrounded by three
atmospheres. The first, nearest the black body of
the sun, is a dense, cloudy covering, possessing high
reflecting power. The second is called the photo-
sphere. It consists of an incandescent gas, and is
the seat of the light and heat of the sun, being the
sun that we see. The third., or outer one, is trans-
parent-very like our atmosphere.
According to this theory, the spots are to be ex-
plained in the following manner. They are simply
openings in these atmospheres made by powerful
upward currents. At the bottom of these chasms,
we see the dark sun as a nucleus at the center, and
around this the cloudy atmosphere-the penumbra.
This explains a black spot with its penumbra. Some-
times the opening in the photosphere may be smaller
than that in the inner or cloudy atmosphere; in that
case there will be a black spot without a penumbra.
It will be natural to suppose that when the heated
gas of the photosphere, or second atmosphere, is
violently rent asunder by an eruption or current
from below, luminous ridges will be formed by the
heaped-up gas on every side of the opening. This
would account for the faculce surrounding the sun-
"* For the views of various authorities on the constitution of the sun, solar spots, etc.,
see Newcomb's Astronomy, third edition, p. 271.


spots. It will be natural, also, to suppose that some-
times the cloudy atmosphere below will close up first
over the dark surface of the sun, leaving only an
opening through the photosphere, disclosing at the
bottom a grayish surface of penumbra. We can

Fig. 19.

Wilson's Theory.

readily see, also, how, as the sun revolving on its
axis brings a spot nearer and nearer to the center,
thus giving us a more direct view of the opening, we
can see more and more of the dark body. Then as
it passes by the center the nucleus will disappear,


until finally we can see only the side of the fissure,
the penumbra, which, in its turn, will vanish.
THE PRESENT THEORY is deduced from the re-
sults of Spectrum Analysis, of which we shall here-
after speak. It is constantly being modified by new
discoveries. But we may, in general, believe the
sun to be a vast, fiery body, surrounded by an
atmosphere of substances volatilized by the intense
heat. Among these, we recognize familiar elements,
as iron, copper, &c.
The different portions of the sun are thought to be
arranged thus: (1). The nucleus, probably gaseous; t
(2). The photosphere, an envelope several thousand
miles thick, which constitutes the visible part of the
sun; (3). The chromosphere, composed of luminous
gas, mostly hydrogen, and the seat of enormous pro-
tuberances, tongues of fire, which dart forth, some-
times at the rate of 150 miles per second, and to a
distance of over 100,000 miles; (4). The corona,t an
outer appendage of faint, pearly light, consisting of
streamers reaching out often several hundred thou-
sand miles. Of these solar constituents, the eye and
the telescope ordinarily reveal only the photosphere;
the rest are seen during a total eclipse or by means
of the spectroscope.
The outer portion of the sun radiates its heat and
"* As Kirchhoff, by his discoveries in Spectrum Analysis, laid the foundation of this
theory, it is often called after him.
t The interior of the sun, if gaseous, must be powerfully condensed, because of the
tremendous pressure of the atmosphere. The high temperature, however, prevents the
gas from liquefying. The rain-storms on the sun, if such ever occur, consist of drops
of molten iron, copper, zinc, &c., vaporized by the enormous heat; and often a tempest
would drive before it this white-hot, metallic blast, with a speed of 100 miles per second.
t This is so called because, during a total eclipse, it forms around the moon a corona,
or glory, that is the most wonderful feature of this rare event. (See p. 141.U


light, and, becoming cooler, sinks; the hotter matter
in the interior then rises to take its place, and thus
convection currents are established (Physics, p. 193).
The cooler, descending currents are darker, and the
hotter, ascending ones are lighter; this gives rise to
the mottled look of the sun. At times, this occurs on
a grand scale, and the heated, up-rushing masses
form the faculae, and the -cooler, down-rushing ones
produce the solar spots.
The Heat of the Sun is generally considered to be
produced by condensation, whereby the size of the
sun is constantly decreasing, and its potential energy
thus converted into kinetic. The dynamic theory
accounts for the heat and the solar spots by assum-
ing that there are vast numbers of meteors revolving
around the sun, and that these constantly rain down
upon the surface of that luminary.* Their motion,
thus stopped, is changed to heat, and feeds this great
central fire. Were Mercury to strike the sun in this
way, it would generate sufficient heat to compensate
the loss by radiation for seven years.
Doubtless, the solar heat is gradually diminishing,
and will ultimately be exhausted. In time, the sun
will cease to shine, as the earth did long since. New-
comb says that in 5,000,000 years, at the present
rate, the sun will have shrunk to half its present
size, and that it cannot sustain life on the earth
more than 10,000,000 years longer. Of this we may
be assured, there is enough to support life on our
globe for millions of years yet to come.
"* The heat of the sun could be maintained by an annual contraction of 220 feet in
its diameter, a decrease so insignificant as to be imperceptible with the best instru-
ments ; or by the annual impact of meteors equal in amount to 1 the mass of Mercury.




The Planets will be described in regular order,
passing outward from the sun. In this journey, we
shall examine each planet in turn, noticing its dis-
tance, size, length of year, duration of day and
night, temperature, climate, number of moons, and
other interesting facts, showing how much we can
know of its world-life in spite of its wonderful dis-
tance. We shall encounter the earth in our imag-
inary wanderings through space, and shall explain
many celestial phenomena already partially familiar
to us.
In all these worlds, we shall find traces of the
same Divine hand, molding and directing in con-
formity to one universal plan. We shall discover
that the laws of light and heat are invariable, and
that the force of gravity, which causes a stone to fall
to the ground, acts similarly upon the most distant
planet. Even the elements of which the planets are
composed will be familiar to us, so that a book of
natural science published here might, in its general
features, answer for use in a school on Mars or
Common Characteristics (Hind). -1. The planets
move in the same direction around the sun; their


course, as viewed from the north side of the ecliptic,
being contrary to the motion of the hands of a
2. They describe elliptical paths around the sun,-
not differing much from circles.
3. Their orbits are more or less inclined to the
ecliptic, and intersect it in two points-the nodes,-
one-half of the orbit lying north, and the other south
of the earth's path.
4. They are opaque bodies, and shine by reflecting
the light they receive from the sun.
5. They rotate upon their axes in the same way
as the earth. This we know by telescopic observa-
tion to be the case with many planets, and by anal-
ogy the rule may be extended to all. Hence, they
have the alternation of day and night.
6. Agreeably to the principles of gravitation, their
velocity is greatest at that part of their orbit nearest
the sun, and least at that part most distant from it ;
in other words, they move quickest in perihelion, and
slowest in aphelion.
Comparison of the two Groups of the Major
Planets. (Chambers.)-Separating the major planets
into two groups, if we take Mercury, Venus, the
Earth, and Mars as belonging to the interior, and
Jupiter, Saturn, Uranus, and Neptune to the exterior
group, we shall find that they differ in the following
1. The interior planets, with the exception of the
Earth and Mars, are not attended by any satellite,
while all the exterior planets have satellites.
2. The average density of the first group consider-



ably exceeds that of the second, the approximate
ratio being 5:1.
3. The mean duration of the axial rotations,, or the
mean length of the day of the interior planets, is
much longer than that of the exterior; the average
in the former case being about twenty-four hours,
but in the latter only about ten hours.
Properties of the Ellipse.-In Fig. 20, S and S' are
the foci of the ellipse; A C is the major axis; B D,
the minor or conjugate axis; 0, the center: or,
astronomically, 0 A is the semi-axis-major or mean

Fig. 20.

s S s

An Ellipse.

distance, 0 B the semi-axis-minor: the ratio of 0 S
to 0 A is the eccentricity; the least distance, S A, is
the perihelion distance; the greatest distance, S C,
the aphelion distance.
Characteristics of a Planetary Orbit.-It will not
be difficult to follow in the mind the additional
characteristics of a planet's orbit. Take two hoops,
and bind them into an oval shape. Incline one


slightly to the other, as shown in Fig. 21. Let the
horizontal hoop represent the ecliptic. Imagine a
planet following the inclined hoop, or ellipse; at a
certain point it rises above the level of the ecliptic :*
this point is called the ascending node, and the op-

Fig. 1.

Plua.itu ry Orbits.

posite point of intersection is termed the descending
node. A line connecting the two nodes is the line of
the nodes. The longitude of the node is its distance
from the first point of Aries, measured on the eclip-
tic, eastward.

Comparative Size of Planets (Chambers). -The following scheme
will assist in obtaining some notion of the magnitude of the planetary
system. Choose a level field or common; on it place a globe two feet
in diameter for the Sun : Vulcan will then be represented by a small
pin's head, at a distance of about twenty-seven feet from the center
of the ideal sun; Mercury by a mustard-seed, at a distance of eighty-two
feet; Venus by a pea, at a distance of 142 feet; the Earth, also, by a pea,
at a distance of 215 feet; Mars by a small pepper-corn, at a distance of
327 feet; the minor planets by grains of sand, at distances varying from
500 to 600 feet. If space will permit, we may place a moderate-sized

Lockyer beautifully says: "We may imagine the earth floating around the sun on
a boundless ocean, both sun and earth being half immersed in it. This level, this plane,
the plane of the ecliptic (because all eclipses occur in it), is used by astronomers as we
use the sea-level. We say a mountain is so far above the level of the sea. The astrono-
mer says the star is so high above the level of the ecliptic.


orange nearly one-quarter of a mile distant from the starting point to rep-
resent Jupiter; a small orange two-fifths of a mile for Saturn; a full-sized
cherry three-quarters of a mile distant for Uranus; and lastly, a plum
1I- miles off for Neptune, the most distant planet yet known. Extending

FZg, .

- .

~------ -

Comparative Size of the Planets.

this scheme, we should find that the aphelion distance o' Encke's comet
would be at 880 feet; the aphelion distance of Donati's comet of 1858 at
six miles; and the nearest fixed star at 7,500 miles.


According to this scale, the daily motion of Vulcan in its orbit would be
4C feet; of Mercury, 3 feet; of Venus, 2 feet; of the Earth, 1Z feet; of
Mars, 1l feet; of Jupiter, 10 inches; of Saturn, 71 inches ; of Uranus, 5
inches ; and of Neptune, 4 inches. This illustrates the fact that the orbital
velocity of a planet decreases as its distance from the sun increases. *
Conjunction of Planets.-The grouping together
of two or more planets within a limited area of the
heavens is a rare event. The earliest record we
have is the one of Chinese origin (p. 6), stating that
a conjunction of Mars, Jupiter, Saturn, and Mercury

Fig. 2S.

Venus and Jupiter in Conjunction, January 30, 1868.

occurred in the reign of the Emperor Chuenhio.
Astronomers tell us that this took place Feb. 28, 2446
B. c., between 10 and 18 of Pisces. There is a very
general impression, however, that this conjunction
was afterward calculated and chronicled in their
records. In 1725, Venus, Mercury, Jupiter, and
If we accept the Nebular Hypothesis (p. 55), we can easily understand the reason
of this; the exterior planets, being made earlier, bad the motion of the nebula during
its earlier stage. The rotation-velocity of the nebula kept increasing, and so, of course,
each planet possessed a higher rate of orbital speed than the preceding one.


Mars appeared in the same field of the telescope. In
1859, Venus and Jupiter came so near each other
that they appeared to the naked eye as one object.
Are the Planets Inhabited ?-This question is one
which very naturally arises, when we think of the
planets as worlds in so many respects similar to our
own. We can give no satisfactory answer. Many
think that the only object God can have in making
a world is to form an abode for man. Our own earth
was evidently fitted up, although perhaps not cre-
ated, for this express purpose. Everywhere about
us we find proofs of special forethought and
adaptation. Coal and oil in the earth for fuel and
light, forests for timber, metals in the mountains
for machinery, rivers for navigation, and level
plains for corn. The human body, the air, light, and
heat are all fitted to one another with exquisite
When we turn to the planets, we do not know but
God has other races of intelligent beings who inhabit
them, or even entirely different ends to attain. Of
this, however, we are assured, that, if inhabited, the
conditions on which life is supported vary much
from those familiar to us. When we come to speak
of the different planets, we shall see (1) how they
differ in light and heat, from seven times our usual
temperature to less than -0100; (2) in the intensity
of the force of gravity, from 24 times that of
the earth to less than ; (3) in the constitution of
the planet itself, from a density 1 heavier than that
of the earth to one nearly that of cork.
The temperature may often sweep downward


through a scale of 2,000 in passing from Mercury
to Neptune. No human being could reside on the
former, while we cannot conceive of any polai inhab-

Fig. 24.

Size of the Sun as seen from the Planets.

itayt who could endure the intense cold of the latter.
At the sun, one of our pounds would weigh over 27
pounds; on our moon, the pound weight would be-


"come only about two ounces; while on Vesta, one of
the planetoids, a man could easily spring sixty feet
in the air and sustain no shock in falling. Yet, while
we speak of these peculiarities, we do not know
what modification of the atmosphere or physical
features may exist on Mercury to temper the heat,
or on Neptune to reduce the cold.
With all these diversities, we must, however, admit
the power of an all-wise Creator to form beings
adapted to the life and the land, however different
from our own. The Power that prepared a world
for us, could as easily and perfectly prepare one for
other races. May it not be that the same love of
diversity, that will not make two leaves after the
same pattern nor two pebbles of the same size, de-
lights in worlds peopled by races as diverse ?*
While, then, we cannot affirm that the planets are
inhabited, analogy would lead us to think that they
are, and that the most distant star that shines in
the arch of heaven may give light and heat to living
beings under the care and government of Him who
enlivens the densest forest with the hum of insects,
and populates even a drop of water with its teeming
millions of animalcules.
Divisions of the Planets.-The planets are divided
into two classes: (1). Inferior, or those whose orbits
are within that of the earth-viz., Mercury, Venus;
(2). Superior, or those whose orbits are beyond that

Astronomers conceive the universe to contain worlds in every possible stage of
development, from the primary, gaseous nebula, to a worn-out, dead globe, like the
moon. At a certain period in its existence, each world may be fitted to support life.
Millions may now be in that condition ; others may be approaching, while others have
passed it.


of the earth-viz., Mars, Jupiter, Saturn, Uranus,
Motions of a Planet as seen from the Sun.-Could
we stand at the sun and watch the movements of the
planets, they would all be seen revolving with dif-
ferent velocities in the order of the zodiacal signs.
But to us, standing on one of the planets, itself in
motion, the effect is changed. To an observed at the
sun all the motions would be real, while to us many
are only apparent. The position of a planet, as seen
from the center of the sun, is called its heliocentric
place; as seen from the center of the earth, its geo-
centric place. When Venus is at inferior conjunc-
tion, an observer at the sun would see it in the oppo-
site part of the heavens from that in which it would
appear to him if viewed from the earth.
Motions of an Inferior Planet.-An inferior planet
is never seen by us in any part of the sky opposite
to the sun at the time of observation. It cannot
recede from him as much as 90, or the circum-
ference, since it moves in an orbit entirely enclosed
by the orbit of the earth. Twice in every revolution
it is in conjunction ( d) with the sun,-an inferior
conjunction (A) when it comes between the earth
and the sun, and a superior conjunction (B) when
the sun lies between it and the earth.
When the planet attains its greatest distance east
or west (as we see it) from the sun, it is said to be at
its greatest elongation.
When passing from B to A it is east of the sun,
and from A to B it is west of the sun. When east of
the sun, it sets later than the sun, and hence is


evening star: when west of the sun, it rises earlier
than the sun, and hence is morning star. An inferior
planet is never visible when in superior conjunction,
as its light is then lost in the greater brilliancy of
the sun. When in inferior conjunction, it some-

Fig. 2,


Conjunctions of Inferior' Planet

times passes in front of the sun, and appears to us as
a round, black spot swiftly moving across his disk.
This is called a transit.
Suppose the earth at A (Fig. 26), and the planet at B.


Now, while the earth is passing to F, the planet will
pass to D,-the are AF being shorter than BD, be.
cause the nearer a planet is to the sun the greater its
velocity. While the planet is at B, we locate it at
C on the ecliptic, in Gemini; but at D, it appears to
us to be at G, in Taurus. So that the planet has

Fiqf. &.

.th' ,g rwTe Motion.

retrograded through an entire sign on the ecliptic,
while its course all the while has been directly for-
ward in the order of the signs; and to an observer at
the sun, such would have been its motion.
planet presents all the phases of the moon. At supe-
rior conjunction, the whole illumined disk is turned
toward us; but the planet is lost in the sun's rays:
\ / '. ,; 2
a Nt ^ "

'^=!" ^ ^ :" J
/~'irf'fd oin
retrgraed hrogh a eniresig on he clitic
while its course ~~~al th hl a ee ietyfr
ward~~ ~~~~ inteodroh ins;adt n bevra

toward us ; but the planet is lost in the sun's rays:


therefore neither Mercury nor Venus ever presents a
complete circular appearance, like the full moon. A
little before or after superior conjunction, an inferior
planet may be seen with a telescope; but the whole
of the light side is not turned toward us, and so the
planet appears gibbous, like the moon between the
first quarter and full. At its greatest elongation,
the planet shows us only one-half its illumined disk;
this decreases, becoming more and more crescent
toward inferior conjunction, at which time the un-
illumined side is toward us.

Fig. 27.

Phases of an Inferior Planet.

Motions of a Superior Planet.-The superior planet
moves in an orbit which entirely surrounds that of the
earth. When the earth is at E (Fig. 28), the planet
at L is said to be in opposition to the sun (8). It
is then at its greatest distance from him-180. The
planet is on the meridian at midnight, while the sun
is on the corresponding meridian on the opposite side
of the earth; or the planet may be rising, when the
sun is just setting. When the planet is at N, it is in


conjunction, and being lost in the sun's rays is invis-
ible to us. When 90 east or west of the sun, the
planet is said to be in quadrature (o).
pose the earth to be at E and the planet at L, and
that we move on to G while the planet passes on to
Fig. 28.

-C N


O--the distance EG being longer than LO, the re
SVN /1

Retrograde Motion qf a Superior Planet.
0-the distance EG being longer than LO, the re-
verse of what takes place in the movements of the
inferior planets; at E, we should locate the planet at
P on the ecliptic, in the sign Cancer; but at G, it
would appear to us at Q, in the sign Gemini, having


apparently retrograded on the ecliptic the distance
PQ, while it was all the time moving on in the
direct order of the signs. Now, suppose the earth
passes on to I and the planet to U, we should then
see it at the point W, further on in the ecliptic than
Q, which indicates direct motion again, and at some
point near Q the planet must have appeared without
After this, it will continue direct until the earth has
completed a large portion of her orbit, as we can
easily see by imagining various positions of the earth
and planet, and then drawing lines as we have just
done, noticing whether they indicate direct or retro-
grade motion. The greater the distance of a planet
the less it will retrograde, as we can perceive by
drawing another orbit outside the one represented in
the cut, and making the same suppositions concern-
ing it as those we have already explained.
Sidereal and Synodic Revolution.-The interval
of time required by a planet to perform a revolution
from one fixed star back to it again, is termed a
sidereal revolution (sidus, a star).
1. The interval of time between two similar con-
junctions of an inferior planet with the earth and
the sun is termed a synodic revolution. Were the
earth at rest, there would be no difference between a
sidereal and a synodic revolution, and the planet
would come into conjunction twice in each revolu-
tion. Since, however, the earth is in motion, it fol-
,lows that, after the planet has completed its sidereal
revolution, it must overtake the earth before they
can both come again into the same position with


regard to the sun. The faster a planet moves, the
sooner it can do this. Mercury, traveling at a
greater speed and on an inner orbit, accomplishes
it much more quickly than Venus. The synodic
period always exceeds the sidereal.
2. The interval between two successive conjunc-
tions or opposition of a superior planet is also
termed a synodic revolution. Since the earth moves
so much faster than any superior planet, it fol-
lows that, after it has completed a sidereal revo-
lution, it must overtake the planet before they can
again come into the same position with regard to
the sun. The slower the planet, the sooner this
can be done. Uranus, making a sidereal revolution
in eighty-four years, can be overtaken more quickly
than Mars, which makes one in less than two
years. It consequently requires over a second
revolution for the earth to catch up with Mars,
only r of a second one to overtake Jupiter, and
but little over -r- of a second one to come up with
Planets as Evening and Morning Stars.-The in-
ferior planets are evening stars from superior to
inferior conjunction ; and the superior planets, from
opposition t6 conjunction. During the other part of
their revolutions, they are morning stars.

Mercury is evening star..... .......... about 2 months.
Venus .. 9
Mars l ......... .. 13 4"
Jupiter .. 6
Saturn ......... (" 6 "
Uranus ...... 6


I. VULCAN (hypothetical),

Supposed Discovery. --Le Verrier, having detected an error in the
assumed motion of Mercury, suggested, in the autumn of 1859, that there
might be an interior planet, which was the cause of this disturbance. On
this being made public, M. Lescarbault, a French physician and an
amateur astronomer, stated that on March 26 of that year he had seen a
dark body pass across the sun's disk, which might have been the
unknown planet. Le Verrier visited him, and found his instruments
rough and home-made, but singularly accurate. His clock was a simple
pendulum, consisting of an ivory ball hanging from a nail by a silk thread.
His observations were on prescription paper, covered with grease and
laudanum. His calculations were chalked on a board, which he planed off
to make room for fresh ones. Le Verrier became satisfied that a new planet
had been discovered by this enthusiastic observer, and congratulated him
upon his deserved success.
On March 20, 1862, Mr. Lummis, of Manchester, England, noticed a
rapidly-moving, dark spot, apparently the transit of an inner planet.
During the total eclipse of July 29, 1878, Professor Watson, of Ann Arbor
Observatory, and Dr. Lewis Swift, of Rochester, claimed to have seen
two Intra-Mercurial planets. As yet, however, the existence of the planet
is not generally conceded. The name Vulcan and the sign of a hammer
have been given to it. Its distance from the sun has been estimated at
13,000,000 miles, and its periodic time (its year) at twenty days.


The fleetest of the gods. Sign, his wand.

Description.-Mercury is nearest to the sun of any
of the definitely-known planets. When the sky is
very clear, we may sometimes see it, just after sun-
set, as a bright, sparkling star, near the western
horizon. Its elevation increases evening by evening,


I. VULCAN (hypothetical),

Supposed Discovery. --Le Verrier, having detected an error in the
assumed motion of Mercury, suggested, in the autumn of 1859, that there
might be an interior planet, which was the cause of this disturbance. On
this being made public, M. Lescarbault, a French physician and an
amateur astronomer, stated that on March 26 of that year he had seen a
dark body pass across the sun's disk, which might have been the
unknown planet. Le Verrier visited him, and found his instruments
rough and home-made, but singularly accurate. His clock was a simple
pendulum, consisting of an ivory ball hanging from a nail by a silk thread.
His observations were on prescription paper, covered with grease and
laudanum. His calculations were chalked on a board, which he planed off
to make room for fresh ones. Le Verrier became satisfied that a new planet
had been discovered by this enthusiastic observer, and congratulated him
upon his deserved success.
On March 20, 1862, Mr. Lummis, of Manchester, England, noticed a
rapidly-moving, dark spot, apparently the transit of an inner planet.
During the total eclipse of July 29, 1878, Professor Watson, of Ann Arbor
Observatory, and Dr. Lewis Swift, of Rochester, claimed to have seen
two Intra-Mercurial planets. As yet, however, the existence of the planet
is not generally conceded. The name Vulcan and the sign of a hammer
have been given to it. Its distance from the sun has been estimated at
13,000,000 miles, and its periodic time (its year) at twenty days.


The fleetest of the gods. Sign, his wand.

Description.-Mercury is nearest to the sun of any
of the definitely-known planets. When the sky is
very clear, we may sometimes see it, just after sun-
set, as a bright, sparkling star, near the western
horizon. Its elevation increases evening by evening,


but never exceeds 280.* If we watch it closely, we
shall find that the planet again approaches the sun
and becomes lost in his rays. Some days after-
ward, just before sunrise, we can see the same planet
in the east, rising higher each morning, until its
greatest elevation equals that which it before at-
tained in the west. Thus the planet appears slowly
but steadily to oscillate like a pendulum, to and fro,
from one side to the other of the sun. The ancients,
deceived by this puzzling movement, failed to dis-
cover the identity of the two stars, and called the
morning star Apollo, the god of day, and the evening
star Mercury, the god of thieves, who walk to and
fro in the night-time seeking plunder. t
On account of the nearness of Mercury to the sun,
it is difficult to be detected.: It is said that Coper-
nicus, an old man of seventy, lamented in his last
moments that, much as he had tried, he had never
been able to see it. In our latitude and climate, we
can generally easily find it if we watch for it at the
time of its greatest elongation, as commonly given
in the almanac.
Motion in Space.-Mercury revolves around the
sun at a mean distance of about 36,000,000 miles. Its

"* This distance varies much, owing to the eccentricity of Mercury's orbit.
t The Greeks gave to Mercury the additional name of "The Sparkling One." The
astrologists looked upon it as the malignant planet. The chemists, because of its
extreme swiftness, applied the name to quicksilver. The most ancient account that we
have of this planet is given by Ptolemy, in his Almagest; he states its location on the
15th of November, 265 B. c. The Chinese also state that on June 9, 118 A. D., it was
near the Beehive, a cluster of stars in Cancer. Astronomers tell us that, according to
the best calculations, it was at that date within less than 10 of that group.
I An old English writer by the name of Goad, in 1686, humorously termed this planet,
" A squinting lacquey of the sun, who seldom shows his head in these parts, as if he
were in debt."


orbit is the most eccentric (flattened) of any among
the eight principal planets, so that,although when in
perihelion it approaches to within about 28,000,000
miles, in aphelion it speeds away 15,000,000 miles
further, or to the distance of over 43,000,000 miles.
Being so near the sun, its motion in its orbit is cor-
respondingly rapid,-viz., thirty miles per second.*
The Mercurial year comprises only about eighty-
eight days, or nearly three of our months. Mercury
is thought to rotate upon its axis in about the same
time as the earth, so that the length of the Mercurial
day is nearly the same as that of the terrestrial
Though Mercury thus completes a sidereal revolu-
tion around the sun in eighty-eight days, yet to pass
from one inferior or superior conjunction to the next
(a synodic revolution) requires 116 days. The reason
of this is, that when Mercury comes around again
to the point of its last conjunction, the earth has
gone forward, and it requires twenty-eight days for
the planet to overtake us.
The Distance from the Earth varies still more
than the distance from the sun. At inferior con-
junction, Mercury is between the earth and the sun,
and its distance from us is the difference between
the distance of the earth and of the planet from the
sun: at superior conjunction, it is the sum of these
distances. Its apparent diameter in these different
positions varies in the same proportion as the dis-
tance, or nearly three to one. The greatest and least

At this rate of speed, we could cross the Atlantic Ocean in two minutes.


distances vary as either planet happens to be in
aphelion or perihelion.*
Dimensions.-Mercury is about 3,000 miles in di-
ameter. Its volume is about A- that of the earth-
i. e., it would require twenty globes as large as Mer-
cury to make one the size of the earth, or 25,000,000
to equal the sun. It is L denser than the earth, its
mass is nearly -6 that of the earth, and a stone let
drop upon its surface would fall 71 feet the first
second. Its specific gravity is not far from that of
tin. A pound weight removed to Mercury would
weigh only about seven ounces.
Seasons.-As Mercury's axis is much inclined from
a perpendicular (perhaps 70), its seasons are peculiar.
There are no distinct frigid zones ; but large regions
near the poles have six weeks of continuous day and
torrid heat, alternating with a night of equal length
and arctic cold. The sun shines perpendicularly
upon the torrid zone only at the equinoxes, while he
sinks far toward the southern horizon at one solstice,
and as far toward the northern horizon at the
other. t The equatorial regions, therefore, during
each revolution, are modified in their temperature
from torrfd to temperate, and the tropical heat is
experienced alternately toward the north and the
south of what we call the temperate zones.
There is no marked distinction of zones as with us,
but each zone changes its character twice during the

If at inferior conjunction Mercury is in aphelion and the earth in perihelion, its
distance from us is only 91,500,000 43,000,000 = 48,500,000 miles. If at superior con-
junction Mercury is in aphelion and the earth in aphelion also, its distance from us
is 94,500,000 + 43,000,000 = 137,500,000 miles.
t Read a chapter entitled "The Fiery World," in Proctor's Poetry of Astronomy,


Mercurial year, or eight times during the terrestrial
one. An inhabitant of Mercury must be accustomed
to sudden and violent vicissitudes of temperature
At one time, the sun not only thus pours down its
vertical rays, and in a few weeks after sinks far
toward the horizon, but, on account of Mercury's

Fig. 29.

Orbit and Seasons of Mercury.

elliptical orbit, when in perihelion the planet ap-
proaches so near the sun that the heat and light are
ten times as great as ours, while in aphelion it re-
cedes so as to reduce the amount to four and a half
times. The average heat is about seven times that
of the earth,-a temperature sufficient to turn water
into steam, and even to melt zinc.


The relative length of the days and nights is much
more variable than with us. The sun, apparently
seven times as large as it seems to us, must be a
magnificent spectacle, and illumine every object
with insufferable brilliancy. The evening sky is,
however, lighted by no moon.
Telescopic Features.-Through the telescope, Mer-
cury presents all the phases of the moon, from a slen-
der crescent to gibbous, after which its light is lost in
that of the sun. These phases prove that Mercury is
spherical, and shines by the light reflected from the
sun. Being an inferior planet, we never see it when
full, and hence the brightest, nor when nearest the
earth, as then its dark side is turned toward us.
Owing to the dazzling light, and the vapors almost
always hanging around our horizon, this planet has
not of late received much attention; the data here
given are mainly based upon the observations of the
older astronomers, and are, therefore, not universally
accepted. Mercury is thought by some to have a
dense, cloudy atmosphere, that materially dimin-
ishes the intensity of its heat and, perhaps, makes
it habitable, though others assert that the atmos-
phere is too insignificant to be detected. Some dark
bands about the planet's equator indicate, perhaps,
an equatorial zone. There are, also, lofty heights
which intercept the light of the sun, and deep valleys
plunged in shade. One mountain is claimed to be
over eleven miles high, or about 2-u the diameter of
the planet.*
The height of the loftiest peak of the Himalayas is only 29,000 feet, or about -- L
part of the earth's diameter.



The Queen of Beauty. Sign 9, a looking-glass.

Description.-Venus, the next in order to Mercury,
is the most brilliant of the planets.* She presents
the same appearances as Mercury. Owing, however,
to the larger size of her orbit, her greatest apparent
oscillations are nearly 480 east and west of the sun,
or about 20' more than those of Mercury. She is
therefore seen much earlier in the morning and
much later at night. She is morning star from in-
ferior to superior conjunction, and evening star from
superior to inferior conjunction.
Venus is the most brilliant about five weeks before
and after inferior conjunction, at which time the
planet is bright enough to cast a shadow at night.
If, in addition, at this time of greatest brilliancy,
Venus is at or near her highest north latitude, she
may be seen with the naked eye in full daylight.
This occurs once in eight years-the interval required
for the earth and planet to return to the same situa-
tion in their orbits; eight complete revolutions of the

"* When visible before sunrise, she was called by the ancients Phosphorus, Lucifer,
or the Morning Star, and when she shone in the evening after sunset, Hesperus, Vesper,
or the Evening Star.
t This distance varies only about 30, owing to the slight eccentricity of Venus's
T Arago relates that Buonaparte, upon repairing to the Luxembourg, when the
Directory was about to give him a fete, was much surprised at seeing the multitude
paying more attention to the heavens above the palace than to him or his brilliant staff.
Upon inquiry, he learned that these curious persons were observing with astonishment
a star which they supposed to be that of the Conqueror of Italy. The emperor himself
was not indifferent when his piercing eye caught the clear lustre of Venus smiling upon
him at midday.


earth about the sun occupying nearly the same time
as thirteen of Venus.
Motion in Space.-Venus has an orbit the most
nearly circular of any of the principal planets. Her
mean distance from the sun is about 67,000,000 miles,
which varies at aphelion and perihelion 1,000,000
miles,-a contrast to Mercury, which varies 15,000,000
Venus makes a complete revolution around the
sun in about 225 days, at the mean rate of twenty-
two miles per second; hence her year is equal to
about seven and one-half of our months. This is a
sidereal revolution, as it would appear to an ob-
server at the sun; a synodic revolution requires 584
Mercury, we remember, catches up with the earth
in twenty-eight days after it reaches the point where
it left the earth at the last inferior conjunction. But
it takes Venus nearly two and a half revolutions to
overtake the earth anu come into the same conjunc-
tion again. This grows out of the fact that. she
has a longer orbit than Mercury, and moves only
about one-sixth faster than the earth, while Mer-
cury travels nearly twice as fast as our planet.
Venus rotates upon her axis in about twenty-four
hours; so the length of her day does not differ essen-
tially from ours.
Distance from the Earth.-Like that of Mercury,
the distance of Venus from the earth, when in in-
ferior conjunction, is the difference between the dis-
tances of the two planets from the sun; when
in superior conjunction, the sum of these distances.

When nearest to us, Venus is only about 25,000,000
miles away.
Figure 30 represents her apparent dimensions at
the extreme, mean, and least distances from us,
The variation is nearly as the numbers 10, 18, and 65.
It would be natural to think that the planet is the
brightest when the nearest, and thus the largest, but
Fig. 80.

Extremen,Mean, and Least Apparent Size of Venus; and her Phases.
we should remember that then the bright side is
toward the sun, and the unillumined side toward us.
Indeed, at the period of greatest brilliancy, of which
we have spoken, only about one-fourth of her light is
visible. At this time, however, observers have
noticed the entire contour of the planet to be of a
dull gray hue, as seen in the cut.
Dimensions.-Venus is about 7,600 miles in diame-
ter. The volume and density of the planet are each
about nine-tenths that of the earth. A stone let fall
upon her surface would fall fourteen feet in the first


second: a pound weight removed to her equator
would weigh about fourteen ounces. From this we
see that the force of gravity does not decrease
exactly in proportion to the size of the planet, any
more than it increases with the size of the sun.
The reason is, that the body is brought nearer the
mass of the small planet, and so feels its attraction
more fully than when far out upon the circumfer-
ence of a large body,-the attraction increasing as
the square of the distance from the particles de-
Seasons.-Since the axis of Venus is very much
inclined from a perpendicular, her seasons are similar

Fig. 31.

Venus at her Solstice.

to those of Mercury. The torrid and temperate zones
overlap each other, and the polar regions have, alter-
nately, at one solstice a torrid temperature, and at
the other a prolonged arctic cold. The inequality of
the nights is very marked. The heat and light are


double that of the earth, while the circular form of
her orbit gives nearly an equal length to her four
If the inclination of her axis is 75, as some as-
tronomers hold, her tropics must be 750 from the
equator, and her polar circles 750 from the poles. The
torrid zone is, therefore, 150 in width. The torrid
and frigid zones interlap through a space of 600, mid-
way between the equator and the poles.
Telescopic Features.-Venus, being an interior
planet, presents, like Mercury, all the phases of the
She is thought to have a dense, cloudy atmosphere.
This was suggested by the fact that at the transit of


Crescent and Spots of Venus.

Venus over the sun in 1761, 1769, and 1882, a faint
ring of light surrounded the black disk of the planet.
This was discovered by Galileo, and was among the first achievements of his tele-
scopic observations. It had been argued against the Copernican system that, if true,
Venus should wax and wane like the moon. Indeed, Copernicus himself boldly declared
that, if means of seeing the planets more distinctly were ever invented, Venus would be
found to present such phases. Galileo, with his telescope, proved this fact, and
thus vindicated the Copernican theory.


The evidence of an atmosphere, as well as of moun-
tains, however, rests upon the peculiar appearance
attending her crescent shape.
1. The luminous part does not end abruptly; on
the contrary, the light diminishes gradually. This
diminution can be explained by a twilight caused by
an atmosphere which diffuses the rays of light into
regions of the planet where the sun is already set.
Thus, on Venus, as on the earth, the evenings are
lighted by twilight, and the mornings by dawn.
2. The edge of the enlightened portion of the
planet is uneven and irregular. This appearance is
doubtless the effect of shadows cast by mountains.
Spots have been noticed on her disk which are con-
sidered to be traceable to clouds. Herschel thinks
that we never see the body of the planet, but only her
atmosphere loaded with vapors, which may mitigate
the glare of the intense sunshine.
Satellites.-Venus is not known to have any

Sign, 4, a circle with Equator and Meridian.

THE EARTH is the next planet we meet in passing
outward from the sun. To the beginner, it seems
strange enough to class our world among the heav-
enly bodies. They are brilliant, while it is dark and
opaque; they appear light and airy, while it is solid
and firm; we see in it no motion, while they are


constantly changing their position; they seem mere
points in the sky, while it is vast and extended.
Yet, at the very beginning, we are to consider the
Fiq. 33.

The Earth in Space.

earth as a planet shining brightly in the heavens,
and appearing to other worlds as a planet does to us.


We are to learn that it is in motion, flying through
its orbit with inconceivable velocity; that it is not
fixed, but hangs in space, held by an invisible
power of gravitation which it cannot evade; that
it is small and insignificant beside the mighty globes
that so gently shine upon us in the far-off sky; that,
in fact, it is only one atom in a universe of worlds,
all firm and solid, and all, perhaps, equally fitted to
be the abode of life.
"Dimensions.-The earth is not "round like a ball,"
but flattened at the poles. Its form is that of an
oblate spheroid. Its polar diameter is about 7,899
miles, and its equatorial about 7,925-. The com-
pression is, therefore, 26- miles. (See table in
Appendix.) If we represent the earth by a globe
one yard in diameter, the polar diameter would be
one-tenth of an inch too long. The circumfer-
ence of the earth is nearly 25,000 miles. Its density
is about 51 times that of water. Its weight is
6,069,000,000,000,000,000,000 tons.
The inequalities of the earth's surface, arising
from valleys, mountains, etc., have been likened to
the roughness on the rind of an orange. On a globe
sixteen inches in diameter, the land, to be in pro-
portion, should be represented by the thinnest writing
paper, the hills by very fine grains of sand, and ele-
vated ranges by thick drawing-paper. To represent
the deepest wells or mines, a scratch should be made
that would be invisible except with a glass.

Were the sun's attractive force upon the earth replaced by the largest steel tele-
graph wire, it would require nine wires for each square inch of the sunward side of our
globe, to hold the earth in her orbit.